UNIVERSITY OF EDUCATION, WINNEBA
COLLEGE OF AGRICULTURE EDUCATION
MAMPONG – ASHANTI
THE EFFICACY OF LUMAX 537.5 SE FOR WEED CONTROL IN
MAIZE FOR MAXIMUM ECONOMIC RETURNS
BY
VINCENT YAO ANORVEY
(808001003)
JUNE, 2011
1
UNIVERSITY OF EDUCATION, WINNEBA
COLLEGE OF AGRICULTURE EDUCATION
MAMPONG – ASHANTI
THE EFFICACY OF LUMAX 537.5 SE FOR WEED CONTROL IN
MAIZE FOR MAXIMUM ECONOMIC RETURNS
A THESIS IN THE DEPARTMENT OF CROPS AND SOIL SCIENCE,
COLLEGE OF AGRICULTURE EDUCATION, SUBMITTED IN THE SCHOOL
OF RESEARCH AND GRADUATE STUDIES IN PARTIAL FULFILMENT OF
THE REQUIREMENT FOR THE AWARD OF MASTER OF PHILOSOPHY
(M.PHIL) IN AGRONOMY IN THE UNIVERSITY OF EDUCATION, WINNEBA
BY
VINCENT YAO ANORVEY
(808001003)
M.ED (EDUC. ADM.); B.ED (AGRIC ED.)
JUNE, 2011
2
DECLARATION
I hereby declare that except for reference to the works of other researchers which have
been duly cited, this work is the result of my own original research and that this thesis has
neither in whole nor in part been presented for another degree elsewhere.
…………………………………………………….
VINCENT YAO ANORVEY (STUDENT)
…………………………………………………….
DATE
…………………………………………………….
PROF. H. K. DAPAAH (PRINCIPAL SUPERVISOR)
…………………………………………………….
DATE
…………………………………………………….
MR. E. K. ASIEDU (CO-SUPERVISOR)
…………………………………………………….
DATE
i
ABSTRACT
Two field studies were conducted at the Multipurpose Crop Nursery research fields of the
University of Education, Winneba, Mampong-Ashanti in the transitional agro-ecological
zone of Ghana from September-December, 2009 and April-July, 2010 to determine the
effects of various rates of Lumax 537.5 SE on weed control in maize and maize growth,
yield and economic benefits. The experimental design used was a randomized complete
block with four replicates. The treatments were Lumax 537.5 SE at rates 2, 4, 6, and
8l/ha. Unweeded and hoe-weeded treatments were added as controls. The maize cultivar,
Akposoe was used. Hoe-weeded and Unweeded control treatments recorded the highest
weed score at 2WAP. However, Hoe-weeded and all Lumax-treated plots gave better
weed control efficiency with lower weed densities and weed dry matter than Unweeded
control treatment. The 4l Lumax/ha was as effective as 6l and 8l Lumax/ha in weed
control. Differences in percentage crop establishment among treatments in both years,
and days to 50% silking in 2009, were not significant. However, 4l, 6l, 8l Lumax/ha and
Hoe-weeded treatments produced similarly taller plants with greater leaf area index and
shoot dry matter than Unweeded control in both years. Differences in 100-seed weight,
grain yield and harvest index among Hoe-weeded and Lumax at 4l/ha, 6l/ha, 8l/ha
treatments were not significant during both cropping seasons. The 4l Lumax/ha gave
marginal rates of returns of 501-714% over the 2l Lumax/ha in both years. The Hoeweeded and Lumax rates at 6l/ha and 8l/ha had lower net benefits, but higher total
variable costs than the 4l Lumax/ha; and therefore were dominated by the latter. It was
concluded that Lumax 537.5 SE at 4l/ha was the optimum rate for effective weed control
ii
in maize, enhanced maize growth and grain yields, and lucrative economic benefits on
maize production in Mampong in the transitional agro-ecological zone of Ghana.
iii
ACKNOWLEDGEMENT
I wish to acknowledge the Almighty God for His grace, support, and splendid guidance
and for the knowledge and wisdom to do this work.
I further wish to express my sincere gratitude to the College of Agriculture Education,
University of Education, Winneba for providing most of the relevant materials and
assistance required for the successful completion of the project.
My greatest appreciation and gratitude go to my supervisor, Prof. H.K. Dapaah and the
co-supervisor, Mr. E.K. Asiedu of the College of Agriculture Education, University of
Education, Winneba who supervised this work and offered valuable criticisms,
corrections and suggestions, despite their tight schedule to enable me complete this work.
I am also grateful to Mr. Attivor who donated two litres of Lumax 537.5 SE on behalf of
Weinco Ghana Ltd. for the field experiments.
To my several friends including Dawuda, Antoinette, Kofi Amponsah, Otabil and those
whose names I cannot mention due to space, I am grateful for your support, pieces of
advice and encouragement.
Finally, my thanks go to Hamza and Theresa (UEW-M) for the time they took to read and
type my script for me. May God bless you all.
iv
DEDICATION
This work is dedicated to Judith my wife, Hellen, Ephraim and Gloria, my children and
Nobert my brother for their support and encouragements.
v
TABLE OF CONTENTS
CONTENT
PAGE
DECLARATION
i
ABSTRACT
ii
ACKNOWLEDGEMENT
iv
DEDICATION
v
TABLE OF CONTENTS
vi
LIST OF TABLES
xi
LIST OF FIGURES
xii
CHAPTER ONE
INTRODUCTION
1
1.1 Background of the Study
1
1.2 Statement of the problem and Justification
2
1.3 Objectives of the Study
6
CHAPTER TWO
LITERATURE REVIEW
7
2.1 Origin and Distribution of Maize
7
2.2 Importance/Uses of maize
8
2.3 Requirements for Maize Growth, Development and Yield
10
2.3.1 Climatic Requirements for Maize
10
2.3.2 Soil Requirements for Maize
12
2.4 Maize - Weed Competitions
14
2.5 Effects of Weeds on Maize Production
20
2.6 The Benefits of Herbicide Use in Maize
22
vi
2.6.1 Herbicides protect environment
23
2.6.2 Herbicides save labour for weed control
24
2.6.3 Herbicides save cropland of erosion
25
2.6. 4 Herbicides control difficult or dangerous weeds
26
2.6.5 Herbicides save energy
27
2.6. 6 Herbicides protect and increase maize production
28
2.7 The Use of Lower Doses of Herbicides
29
2.8 Composition, Characteristics and Efficacy of Lumax
31
2.9 Effects of Weed Control Methods on Weed Assessments in Maize
36
2.9.1 Weed Density in Maize
36
2.9.2 Maize Phenology
42
2.9.3 Maize Yield and Yield Components
42
2.10 Effects of Herbicides on Economic Benefits in Maize Production
47
CHAPTER THREE
MATERIALS AND METHODS
49
3.1 Experimental Site/Location Description
49
3.2 Experimental Design and Treatments
49
3.3 Cultivation and Management Practices
50
3.3.1 Land Preparation
50
3.3.2 Planting/ Sowing
50
3.3.3 Fertilization
51
3.4 Data Collected
51
3.4.1 Climatic Data Collected
51
3.4.2 Soil Preparation and Analysis
51
3.4.3 Weeds Assessment
52
3.4.4 Vegetative Growth of Maize
54
3.4.5 Maize Yield and Yield Components
55
3.4.6 Economic Returns or Partial Budget Analysis
56
vii
3.5 Data Analysis
57
CHAPTER FOUR
RESULTS
58
4.1 Climatic Conditions at the Site
58
4.2 Soil Characteristics
60
4.3 Weeds Assessments
60
4.3.1 Weed Score
61
4.3.2 Percentage Weed Control
62
4.3.3 Weed Control Efficiency
62
4.3.4 Weed Density
63
4.3.5 Weed Flora
64
4.3.6 Weed Dry Matter
66
4.4 Vegetative Growth of Maize
67
4.4.1 Percentage Crop Establishment
67
4.4.2 Leaf Area Index at Tasseling
68
4.4.3 Days to 50% Silking
68
4.4.4 Plant Height
69
4.4.5 Maize Shoot Dry Matter
70
4.5 Yield and Yield components of Maize
71
4.5.1 100-Seed weight
71
4.5.2 Grain Yield
72
4.5.3 Harvest Index
72
4.6 Correlation between maize grain yield and yield component, weed
and weed control variables
73
4.7 Economic Analysis
74
CHAPTER FIVE
5.0 DISCUSSIONS
77
5.1 Climatic Conditions at the Site
77
5.2 Physico-chemical properties of soil
78
viii
5.3 Weeds Assessment
79
5.3.1 Weed Score
79
5.3.2 Percentage Weed Control and Weed Control Efficiency
82
5.3.3 Weed Control Efficiency
84
5.3.4 Weed Density
84
5.3.5 Weed Flora
86
5.3.6 Weed Dry Matter
88
5.4 Vegetative Growth of Maize
90
5.4.1 Crop Establishment
90
5.4.2 Leaf Area Index
92
5.4.3 Days to 50% Silking
93
5.4.4 Plant Height
94
5.4.5 Maize Shoot Dry matter
96
5.5 Yield and Yield components
97
5.5.1 100-Seed Weight
97
5.5.2 Harvest Index
98
5.5.3 Grain Yield
99
5.6 Economic or Partial Budget Analysis
102
CHAPTER SIX
SUMMARY, CONCLUSIONS AND RECOMMENDATIONS
105
6.1 Summary
105
6.2. Conclusions
107
6.3 Recommendations for Future Research
108
REFERENCES
109
ix
APPENDICES
Appendix 1: Guide to Interpretation of Soil Analytical Data
132
Appendix 2: Percentage Composition of Life Form Category and Dominant
Species of Weeds, 2009
133
Appendix 3: Percentage Composition of Life Form Category and Dominant
Species of Weeds, 2010
134
Appendix 4: Information used for the partial budget analysis, 2009 and 2010
x
135
LIST OF TABLES
TABLE
PAGE
Table 4.1: Climatic conditions during 2009 cropping season
59
Table 4.2: Climatic conditions during 2010 cropping season
59
Table 4.3: Physico-chemical properties of soil at the experimental site, 2009
and 2010
60
Table 4.4: Weed score, percentage weed control and weed control efficiency as
affected by Lumax rates, 2009 and 2010
61
Table 4.5: Weed Flora as affected by Lumax Rates in 2009 and 2010
65
Table 4.6: Weed dry matter as affected by Lumax rates in 2009
66
Table 4.7: Maize crop establishment, leaf area index and days to 50% silking as
affected by Lumax rates in 2009 and 2010
68
Table 4.8: Maize Shoot Dry Matter (g/m2) as affected by Lumax rates and
hoe-weeding, 2009
70
Table 4.9: 100-Seed weight, grain yield, % grain yield increases and harvest
index influenced by Lumax and hoe-weeding, 2009 and 2010
71
Table 4.10: Correlation between maize grain yield and weed, maize growth and
yield component variables
75
Table 4.11: Partial budget analysis for maize as affected by Lumax 537.5 SE
rates and hoe weeding, 2009
76
Table 4.12: Partial budget analysis for maize as affected by Lumax 537.5 SE
rates and hoe weeding, 2010
76
xi
LIST OF FIGURES
FIGURE
PAGE
Fig.4.1 Weed density as affected by Lumax rate and hoe-weeding-2009
63
Fig.4.2 Weed density as affected by Lumax rate and hoe-weeding-2010
63
Fig. 4.3 Fig.4.4 Effect of Lumax rates and hoe-weeding on plant height-2009
69
Fig.4.4 Effect of Lumax rates and hoe-weeding on plant height-2010
69
xii
CHAPTER ONE
INTRODUCTION
1.1 Background of the Study
Maize (Zea mays L), belongs to the grass family Gramineae, it is believed to have
originated from Mexico or Central America, and spread to West Africa with early
European traders in the 16th century (Tweneboah, 2000). It is the most important cereal
crop in the sub-Saharan Africa, and the third most important cereal in the world after rice
and wheat. In West Africa, maize is perhaps the most important cereal as it forms the
major staple for most communities or households. It is estimated that 75% of the total
production of maize is used as food by farmholds or communities and the remaining finds
its way into starch manufacturing industry, poultry feed and food grain sales
(Muhammad, 1979).
In Ghana, maize is the most important grain crop produced throughout the country under
diverse environments. It accounts for about 50-60% of the country’s cereal production,
and is a major staple for most household or communities playing a critical role in
ensuring food security. It is an important source of carbohydrate, iron, vitamin B and
minerals. The regional contributions to national total maize production in Ghana are 22%,
33%, 31% and 14% from the coast, forest, southern savanna and northern savanna,
respectively (IFPRI, 2008). The FAO data ranked Ghana as the 49th country worldwide
for its production of 950,000 metric tonnes of maize with an average of 1.27 metric
tonnes/hectare covering 750,000 hectares in 2003 (NUEweb, 2007). FAOSTAT (2011)
showed that Ghana produced 1,100,000 metric tonnes of maize in 2008. In 2009 the total
1
domestic production of maize in Ghana amounted to 1,619,600 metric tonnes (Mensah,
2010). Maize constitutes 20% of Ghana’s total agricultural GDP (NUEweb, 2007).
Nationwide, maize accounts for 16.8% of the revenues from crop sales earned by poor
households and 18.5% of revenues from crop sales earned by “hardcore poor households”
(Boateng et al., 1990).
Weed control in the fields of maize is very essential for obtaining good yield. Khan et al.
(1998) observed that weed control practices resulted in 77-97% higher yield than the
weedy check. Chikoye et al. (2005) also found that inadequate weed control in maize,
especially during the first 6 weeks after sowing (WAS) resulted in maize yield losses
ranging fron 50% to 90%. Lumax 537.5 SE, a selective pre-emergence herbicide is a
suspoemulsion that owes its origin to the discovery of a natural herbicide secreted by the
Callistemon plant (Syngenta, 2005). Lumax is developed by Syngenta Company for the
control of annual grass and broadleaf weeds in field corn, field production seed corn,
field silage corn, sweet corn, yellow popcorn, and certain other crops. Its active
ingredients are S-metolachlor (29.40%), Atrazine (11.00%), Mesotrione (2.94%) and
other ingredients (56.66%) (Syngenta, 2009).
1.2 Statement of the Problem and Justification
Maize production is constrained among other factors by poor crop management, notably
inadequate weed control especially during the first six weeks after sowing resulting in
maize yield losses ranging from 50% to 90% (Chikoye et al., 2005). Yield reduction in
maize results from high competition between the crop and weed for water, light, nutrients
2
and carbon dioxide (Tollenaar et al., 1997a) especially when the competing weeds are of
the same family with maize. While the average yield of maize in developed countries can
reach up to 8.6 tonnes per hectare, production per hectare is very low (1.3 tonnes per
hectare) in developing countries (IITA, 2007). Maize yield in farmers’ fields in Ghana
are often less than 1 tonne per hectare, while the maize cultivars have a potential of more
than 4 tonnes per hectare (Aflakpui et al., 2005).
Yield losses estimates due to weeds vary considerably worldwide depending on the weed
species, intensity of weed population, competitive ability of the crop, duration of weed
infestation, soil fertility, climatic conditions, edaphic and management factors (Kondap et
al., 1980; Minjas and Jana, 1983; Rao, 1983). The first six weeks after planting are
critical in controlling weeds in maize. Maize is most sensitive to weed competition
during the early phase of its growth as it grows slowly during the first 3 to 4 weeks
(Sandhu et al., 1986). Weeds not controlled within two weeks after maize emergence can
cause grain losses between 35 and 70% (Khan et al., 1998). Worldwide maize production
is hampered up to 40 percent by competition from weeds which are the most important
pest group of this crop (Oerke and Dehne, 2004). Weeds interfere with harvesting and
increase the cost involved in crop production. Overall, weeds have the highest loss
potential (37%) which is higher than pathogens (16%) and viruses (2%) (Oerke, 2005).
Reduction in maize yield due to weed infestation translates into hunger, disease, reduced
farmer income and adverse effects on a country’s development budget because money
needed for development may have to be used for importation of maize to redress any
short-fall.
3
Farmers undertake weed control, but it is one of the most labour intensive activities for
small-scale farmers especially in areas where high temperature and regular rainfall
encourage rapid weed growth (Hillocks, 1998).Weeds can be controlled by cultural,
biological and chemical measures. Although, cultural methods are still useful tools they
are laborious, time consuming and expensive, especially when labour problem is
becoming severe day by day.
Hand hoe weeding when done timely twice or thrice, or the use of herbicides have
controlled weeds effectively in maize (Mathews, 1984; Chikoye et al., 2002). However,
the use of the hand hoe is time-consuming, back-breaking and expensive especially
where labour is scarce. In the hand hoe system, weeding alone accounts for 40-54% of
the total labour input in farming in Ghana, Nigeria, Burkina Faso, Sierra Leone, Malawi,
Zambia, Ethiopia and Tanzania, requiring 300-400 man- hours per hectare (Zimdahl,
1983). In most cases due to limitations on family labour, farmers are unable to do their
weeding on time.
Considering the limitations of cultural methods of weed control, chemical weed control is
an important alternative. Herbicide application is an efficient way to check weed
infestation that helps achieve speedy breakthrough for increasing maize production
(Naveed et al., 2008).
Several reports have addressed the importance of herbicides use in maize. Miller and
Libby (1999) have reported that corn yield responded positively when weeds were
controlled by herbicides. Becker and Staniforth (1981) obtained higher yield in maize
4
with herbicides as compared to cultural weed control. Jehangeri et al. (1984) reported
that application of selective herbicides provided 65 to 90% weed control and gave 100150% more maize yield than the weedy check. In maize, mechanical weed control was
25% to 44% less effective than that obtained with herbicides and gave a yield reduction
from 6% to 18% (Balsari, 1993).
Weed control in maize through the use of herbicides has received little attention in West
Africa, and particularly in Ghana, while elsewhere in the world herbicides have shown a
promise in weed management in maize. In Ghana, the few farmers who apply some
herbicides do not apply adequate amounts of the recommended rates, citing the high cost
of the input (Aflakpui et al., 2005).
Proper selection of herbicides, proper time of application and proper dose of herbicides
are the important consideration for lucrative return on maize production (Fayad et al.,
1998). The use of herbicides with maize in Ghana may be of great help to the farmer.
Several pre–emergence herbicides are being used for weed control in maize in Ghana.
However, Lumax 537.5 SE containing Atrazine, S-Metolachlor and Mesotrione, is one of
the most recently developed pre-emergence herbicides that has been introduced into the
Ghanaian market to compete with the already existing ones for use in maize production.
Lumax has been applied at various rates in Nigeria (Chikoye et al., 2009). Lumax’s
manufacturer, Syngenta recommends that Lumax should be applied at 7l/ha,but in soils
with less than three percent organic matter, Lumax should be applied at 5.9l/ha
(Syngenta, 2009). However, Guy (1987) suggested that, the application of herbicides in
each region must be scrupulously examined in the light of the cultivation system in use,
5
the soil, rainfall and existing species of weeds. It has therefore, become necessary to
assess the efficacy of various rates of Lumax 537.5 SE in weed control and their resultant
effects on maize growth and yield in the transitional zone of Ghana in order to adapt the
use of the herbicide to local conditions.
The application rate of Lumax 537.5 SE pre-emergence herbicide that excels best in weed
control and its subsequent enhancement of maize growth and yield and economic returns
may be identified and recommended to herbicide importers and maize farmers in the
transitional zone of Ghana to enable them make informed decisions.
1.3 Objectives of the Study
The main objective of this study was to determine the optimum rate of application of
Lumax 537.5 SE pre-emergence herbicide for effective weed control in maize fields and
its subsequent effect on yield and economic returns in the transitional agro-ecological
zone of Ghana.
The specific objectives of the study were to:
(i)
Determine the effect of different application rates of Lumax 537.5 SE on
weed population in a maize field.
(ii)
Assess the effects of various rates of Lumax 537.5 SE on the vegetative
growth, yield and yield components of maize.
(iii)
Determine the economic returns on maize production using the various rates
of Lumax 537.5 SE.
6
CHAPTER TWO
LITERATURE REVIEW
2.1 Origin and Distribution of Maize
Maize was domesticated in southern Mexico around 4000 BC. When the Europeans
arrived in the Americas, maize had already spread from Chile to Canada. Maize was
reported for the first time in West Africa in 1498, six years after Columbus discovered
the West Indies (Badu-Apreku et al., 2003). The Portuguese brought floury grain types
from Central and South America to São Tomé, from where they spread to the West
African coast. Through the trans-Saharan trade, the Arabs traders introduced the flinty
maize types that had been brought to northern part of West Africa while the floury types
prevail in the southern parts, with some variation from this pattern.
Maize has extremely wide distribution. It is grown from Latitude 58oN in Canada and
Russia, throughout the tropics, to latitude 42oS in New Zealand and Southern America,
and in areas below sea level in the Caspian Plain up to areas as high as 3800m in Bolivia
and Peru (Badu-Apraku et al., 2003). It is grown in all countries of Africa, from the coast
through savanna regions to the semi-arid regions of West-Africa, and from sea-level to
the mid, and high-altitudes of East and Central Africa (Brink and Belay, 2006).
Currently, maize is widely cultivated throughout the world, and a greater quantity of
maize is produced each year than any other grain. Over 150 million hectares of maize
were planted worldwide, with a yield of 4970.9 kilogram/hectare in 2007 (Wikipedia,
7
2009). The area planted to maize in West and Central Africa alone was 8.9 million
hectares in 2005 with a yield of 10.6 million metric tonnes in 2005 (IITA, 2007).
2.2 Importance/Uses of maize
Maize (Zea mays L.), or corn, is the most important cereal crop in sub-Saharan Africa
and, with rice and wheat, becomes one of the three most important cereal crops in the
world. Maize (Zea mays L.) is the most important grain crop in Ghana and is produced
throughout the country under diverse environments. In industrialized countries, maize is
largely used as livestock feed and as a raw material for industrial products, while in
developing countries, it is mainly used for human consumption.
In developed countries, maize is consumed mainly as second-cycle produce, in the form
of meat, eggs and dairy products. In developing countries, maize is consumed directly
and serves as staple diet for some 200 million people [Department of AgricultureRepublic of South Africa (DARSA), 2003]. In sub-Saharan Africa, maize is a staple food
for an estimated 50% of the population. It is an important source of carbohydrate, protein,
iron, vitamin B, and minerals. Hamayun (2003) noted that maize grain is a valuable
source of protein (10.4%), fat (4.5%), starch (71.8%), fiber (3%), vitamins and minerals
like Ca, P, S and small amounts of Na. Its flour is considered to be a good diet for heart
patients due to its low gluten (protein) content (Hamayun, 2003). The endosperm
contains approximately 80 % of the carbohydrates, 20 % of the fat and 25 % of the
minerals, while the embryo contains about 80 % of the fat, 75 % of the minerals and 20
% of the protein found in the kernel (DARSA, 2003).
8
Africans consume maize as a starchy base in a wide variety of porridges, pastes, grits,
and beer. A thin porridge (‘uji’ in East Africa, ‘ogi’ in Nigeria, ‘koko’ in Ghana) is also
commonly eaten especially as weaning food. Green maize (fresh on the cob) is eaten
parched, baked, roasted or boiled; playing an important role in filling the hunger gap after
the dry season (IITA, 2007). Most people regard maize as a breakfast cereal. However, in
a processed form it is also found as fuel (ethanol) and starch. Starch in turn is
enzymatically converted into products such as sorbitol, dextrine, sorbic and lactic acid,
and appears in household items such as beer, ice cream, syrup, shoe polish, glue,
fireworks, ink, batteries, mustard, cosmetics, aspirin and paint. Maize is high yielding,
easy to process, readily digested, and cheaper than other cereals. It is also a versatile
crop; growing across a range of agro-ecological zones.
Every part of the maize plant has economic value: the grain, leaves, stalk, tassel, and cob
can all be used to produce a large variety of food and non-food products (IITA, 2007).
The stalks are used for fuel, fodder and thatching and as compost. The fibre in the stems
and the inner leaves surrounding the cob are made into paper. These cob leaves are often
used to wrap foods, and may also be made into cloth or mats, and be used for mattress
filling. Ash of the burnt stem is sometimes a substitute of salt (Brink and Belay, 2006).
The starch part of the kernel is used in foods and many other products such as adhesives,
clothing, and pharmaceutical tablets and in paper production. The starch can be converted
into sweeteners and used in products such as soft drinks, sweets, bakery products and
9
jams. The oil from the embryo is used in cooking oils, margarine and salad dressings. The
protein, hulls and soluble part of the maize kernel are used in animal and poultry feed.
2.3 Requirements for Maize Growth, Development and Yield
2.3.1 Climatic Requirements for Maize
Maize needs a regular supply of water and suffers badly in times of drought. It requires
rainfall of about 600-1,200mm per annum and this must be well distributed throughout
the year (Awuku et al., 1991). DARSA (2003) noted that about 15.0 kg of grain are
produced for each millimetre of water consumed. At maturity, each plant will have
consumed 250l of water in the absence of moisture stress (DARSA, 2003). According to
Awuku et al. (1991), maize needs water particularly at the time of tasselling and silking.
During the silk appearance and pollen shedding growth stage, demand for nutrients and
water is high (DARSA, 2003).
The best maize growing areas in West Africa have minimum rainfall of 1,000-1,300mm
per annum, well-distributed during the growth period (Tweneboah, 2000). Certain growth
periods are particularly important if severe reduction in yield is to be avoided. In
particular, Tweneboah (2000) identified the tasselling-to- silking stage as critical, for
grain formation is initiated during this short period. Availability of soil moisture at the
time of tasselling is essential for the production of high yields (Tweneboah, 2000).
Experiments in a number of countries have demonstrated that soil moisture deficiency
that causes wilting for 1-2 days during tasselling can reduce yield up to 20%, and 6-8
days of wilting at this stage can reduce yield by 50% which cannot be made up by later
availability of soil moisture either by precipitation or irrigation (Tweneboah, 2000). The
10
findings of Tweneboah (2000) and DARSA (2003) support that of Adjetey (1994) which
noted that to obtain high yields, it is most important that water deficits do not occur just
prior to tasselling till completion of grain filling. Of all the growth stages, this is the most
sensitive period to water shortage as far as grain yield is concerned (Adjetey, 1994).
Gana et al. (2008) reported that yield obtained from 1995 wet season was generally lower
by 31% than that obtained from 1996 wet season. Gana et al. (2008) noted that the low
yield in 1995 was probably due to low volume of rainfall during the vegetative stage of
the crop life cycle.
Temperature strongly influences the development of maize and hence the time required to
reach maturity. Maize is a warm weather crop and is not grown in areas where the mean
daily temperature is less than 19 ºC (DARSA, 2003). Germination (including imbibitions
of water and elongation of embryo) is strongly temperature dependent. The minimum
temperature for germination is 10 ºC. At 20 ºC, maize should emerge within five to six
days. After seedling emergence, high soil and air temperatures accelerate leaf initiation
(DARSA, 2003).
The maximum rates of shoot and radicle elongation are achieved around 30oC but
elongation ceases at temperatures below 90C and above 400C (Adjetey, 1994). Thus soil
temperature during the first few weeks after sowing is a relevant growth limiting factor in
maize growing areas outside the tropics. High temperature and low moisture result in
pollen being shed before silk is receptive or death of tassel and drying of silk (Adjetey,
11
1994). Maximum plant yields are obtained when temperatures of the late vegetative and
reproductive phases are relatively lower than 30°C (Adjetey, 1994).
According to Awuku et al. (1991), maize requires an average temperature of 13-40°C and
does not grow at higher temperatures. Tweneboah (2000), however, stated that the
optimum temperature for maize growth ranges from 18-21°C.
Although grains have reached physiological maturity, they must dry out before reaching
biological maturity. Under favourable conditions, drying takes place at approximately 5
% per week up to the 20 % level, after which there is a slowdown (DARSA, 2003).
No other crop utilizes sunlight more effectively than maize, and its yield per ha is the
highest of all grain crops. At maturity, the total energy used by one plant is equivalent to
that of 8 293 15 W electric globes in an hour (DARSA, 2003). The aspect of light that
influences maize growth substantially is the amount of light (intensity) received during
the growth period. Maize requires a lot of clear sunshine (Adjetey, 1994).
2.3.2 Soil Requirements for Maize
The most suitable soil for maize must be deep, well drained and have favourable physical
properties, an optimal moisture regime, sufficient and balanced quantities of plant
nutrients and chemical properties that are favourable specifically for maize production
(DARSA, 2003). Maize grows satisfactorily in a variety of soil but requires well –
drained, deep loams or silty loams with high to moderate organic matter and nutrient
content and reaction of pH 5.5- 7.5 for best production (Safo, 1994; Tweneboah, 2000).
12
Adjetey (1994) stated that maize grows on a wide variety of soils, but it prefers deep
fertile well-drained loam and silt loam with the soil pH not less than 4.5.
Maize does not like water-logged soils. Tweneboah (2000) noted that the optimum
moisture content of the soil should be approximately 60 % of soil capacity.
Hamayun (2003) observed that rate of germination mainly depended upon time of
sowing, water, air and temperature. All these factors were almost similar in this case.
Hamayun (2003) noted that differences in mean germination might be due to soil
moisture differences.
Through competition for nutrients, weeds can reduce the growth and yields of maize by
influencing the availability of soil water (Thomas and Allison, 1975; Marais, 1985;
Twomlow et al., 1997). This, results, among other effects, in the temporary
immobilisation of nutrients in the plough layer (Marais, 1985).
According to Baffour (1990), maize normally does very well on moist soil and does
badly on pure clayey or sandy soils. The best soils for maize are normally loams and
loamy soils rich in humus. Ristanovic (2001) in Raemaekers (2001) stated that the ideal
soil for maize is a deep, medium- textured, well-drained fertile soil with a high waterholding capacity. Clayey and sandy soils are not conducive for its growth. However
maize is grown on a wide variety of soils and give high yields if the crop is well managed
(Raemaekers, 2001). Although large-scale maize production takes place on soils with a
clay content of less than 10 % (sandy soils) or in excess of 30 % (clay and clay-loam
13
soils), the textural classes between 10 and 30 % have air and moisture regimes that are
optimal for healthy maize production (DARSA, 2003).
Akobundu (1987) reported that soil texture and organic matter were the most important
factors which influenced herbicide activity in soils. Similarly, it was reported that high
clay and organic matter levels of the soil adsorbed some fraction of applied herbicide and
rendered it unavailable for plant uptake and herbicidal activity (Ayeni and Yakubu,
1995). On the other hand, low carbon in the soil of a maize field in Ibadan made the
applied herbicide available for optimum uptake (Makinde and Ogunbodede, 2007).
Maize is quite tolerant of salt during germination; increasing salinity delays germination
but up to a point, it has no detrimental effect on the percentage of emergence
(Raemaekers, 2001). On the whole, maize is considered to be relatively sensitive to
salinity and is not suited for growing in saline soils or irrigating with saline water
(Raemaekers, 2001).
2.4 Maize- Weed Competitions
The reduction in maize yield due to the presence of weeds is attributed to the crop weed
competition for water, light and nutrients (Silva et al., 2004). Causes of high weed
competition include poor manual weed control, weeding too late, ineffective herbicide
application, delayed planting after land preparation, problem weed species not controlled
by weed control method used, presence of allelopathic weed and very high load of weed
seeds, if the land has been used for continuous maize cropping for many years
14
(CIMMYT, Int, 2005). Maize plants show pronounced competition among themselves
and with the weeds, resulting in low yields. If this competition is intense then large
number of plants will fail to produce seeds, while the production will dwindle in others
(Hamayun, 2003).
The importance of weed competition in maize depends on four factors: the crop growth
stage, the amount of weeds present, the degree of water and nutrient stress, and the weed
species. Weeds damage the crop primarily by competing for light, water, and nutrients.
When infested by weeds, maize develops stress symptoms earlier due to the lack of water
than when it is weed-free (Tollenaar et al., 1997a). However, there are no differences
between soil water contents in maize with and without weeds (Tollenaar et al., 1997a),
but Thomas and Allison (1975) had observed that the water content in maize plots
infested with weeds was greater than in maize plots without weeds. Thus, in the presence
of weeds, the water stress symptoms may not be caused by water availability, but by a
poor ability of the root system to absorb water. Maize grown in the presence of weeds
would have a less developed root system than when grown without weeds. Another
possibility would be that weed root exudates contain toxins that could inhibit root growth
in maize (Rajcan and Swanton, 2001).
Nitrogen deficiency symptoms develop earlier in maize infested with weeds than in
maize kept weed-free. This would imply in soil N depletion in maize grown with weeds,
since maize yield reductions due to weeds are lower under high nitrogen rates than under
lower rates (Rajcan and Swanton, 2001). For instance, Tollenaar et al. (1997a) verified
that, under limiting nitrogen conditions, maize yield was reduced due to weeds by 47%.
15
Under higher levels of N, the reduction was only 14%. However, another aspect must be
involved.
Thomas and Allison (1975) verified that the maize root system becomes less developed
in the presence of weeds. Thus, a smaller root system would be less efficient in absorbing
nutrients. Little is known about the P and K interaction effects on the influence of weed
competition with maize (Rajcan and Swanton, 2001), but the occurrence of processes
similar to those occurring with nitrogen is likely.
The amount and quality of light are involved in the competition for this resource. The
amount of light determines photosynthetic activity, while its quality influences plant
morphology (Rajcan and Swanton, 2001). In maize, most of the light is intercepted by the
younger and more efficient leaves, located above the ear, with less than 10 % of the
photon flux density (PFD) reaching the leaves below 1 m. On the other hand, most
weeds, during and after blooming, are below 1 m. Thus, the direct competition between
maize and weeds for the incident photon flux is relatively small. Even in weed-free maize
fields, the leaves below the ear are older and shaded by the upper leaves. Consequently,
their photosynthetic rates are smaller than the rates observed in the upper leaves. This
means that the maize yield loss due to weed competition for the incident photon flux
cannot be explained by the reduced photosynthetic rates in the bottom leaves, which are
shaded by weeds.
The leaf area index (LAI) defines a plant's ability to intercept the incident photon flux
and is an important factor in determining dry matter accumulation (Rajcan and Swanton,
2001). It has been verified (Tollenaar et al., 1997b) that high competition by weeds
16
reduced the LAI in maize at blooming by 15%. Thus, grain yield losses resulting from
competition for light are better explained by the reduction in LAI than by lower
photosynthetic rates in shaded leaves (Rajcan and Swanton, 2001).
The bottom leaves are not only exposed to a reduced amount of PFD, but also receive
light with a quality that is different from the light received by leaves bathed in full
sunlight. The light inside the canopy is rich in ultraviolet radiation (730 to 740 nm). This
is caused by the selective absorption of red light (660-670 nm) by the photosynthetic
pigments and by the reflection of far-red light by green leaves. This makes the far-red/red
ratio (FR/R) greater in the lower section than in the upper section of the canopy. The
FR/R ratio plays an important role in the induction of many morphological changes in
plant architecture (stem elongation, apical dominance, reduced branching, thinner leaves,
leaf area distribution, etc.) (Salisbury and Ross, 1991). Consequently, plants that develop
under FR-rich light tend to have an architecture that is different from plants that grow
under full sunlight. Shaded plants tend to allocate a greater leaf area in the upper section
of the canopy where more light is available, while plants grown under full sunlight have a
more pyramidal leaf area distribution, which limits shading on the bottom leaves by the
upper leaves (Rajcan and Swanton, 2001).
It has been demonstrated that, at least during the early stages of crop-weed competition,
weeds located closest to the crop row are most critical to crop growth (Carson, 1987).
Maize grain yields can be maintained if weeds growing within the crop row are removed
initially with inter-row weeds removed later before exerting competition effects when
labour shortage is not critical (Rambakudzibga et al., 2002).
17
In studies under controlled conditions, Rambakudzibga et al. (2002) reported that maize
height was not significantly influenced by E. indica competition at 21 days after crop
(maize) emergence (ACE). However, at 42 days ACE, the effect of E. indica competition
on maize height was evident. According to Akobundu (1987), there is an initial period in
the growth of both weeds and crops when negative interaction is absent. This period was
quite evident in the confined drum environment. Similarly, under field conditions, maize
height, maize leaf area and maize cob counts were not significantly affected by weed
competition when weeds were removed as late as 8 weeks ACE (Rambakudzibga et al.,
2002). These authors however, suggested that weeds should be removed within four
weeks ACE to avoid grain yield reduction. Grain yield, therefore appears to be more
sensitive to weed competition effects than other maize developmental attributes.
Furthermore, Rambakudzibga et al. (2002) reported that although the treatment in which
weeds competed with the maize plants from within the crop row constituted only 50% of
the weed pressure of other treatments, weed competitive effects of this treatment
significantly reduced maize grain yields. Weeds located furthest from the crop-row (i.e.,
40 cm) had less competitive effects to the maize plants as reflected in the grain yield
gains (Rambakudzibga et al., 2002). However, in the rainy season under natural weed
infestation, and also under conditions of favourable rainfall conditions, weeds competing
from a distance of 20 cm adversely affected maize grain yield than those competing from
40 cm. They concluded that a weed-free area of 20 cm on either side of the maize row is
too narrow to avoid early weed competition.
18
Maize competitive ability greatly depends on maize stand density and the speed of
development. Because of this, farmers have to consider carefully if their maize crops
have, or will have a good competitive ability. There are also great differences in
competitive ability of maize hybrids (Ford and Pleasant, 1994). In case that they are not
able to assure the good competitive ability of maize, they should not practice weed
control with use of lowered herbicide doses. By using sub-lethal doses, weeds are not
controlled totally (incomplete weed kill). After a relatively short period, they can regrow
if they are not additionally suppressed by maize (Lešnik, 2003). In some environmental
and production conditions, usually the good competitive ability of maize can be reached
in stands where density exceeded 8 plants per m2 (Lešnik, 2003). He concluded that, in
the case of broadcast application the reduction of herbicide doses by 10–25% would be
adequate if weed population consists of less than 100 plants per m2. The findings of
Lešnik (2003) were similar to the results of some researchers (Mulder and Doll 1993;
Rola et al., 1999; Zhang et al., 2000) who also reported that 15–30% reductions of
herbicide doses could be recommended to maize producers when they have to control
moderate weed populations and maize has good competitive ability.
Some weed species cause more damage than others. This can be because the weeds
actually produce toxic substances which damage the crop (allelopathy) or because the
weeds are very effective competitors for water or nutrients (Duke, 1985).
Two types of approaches are utilized in most competition studies between weeds and
maize (Rajcan and Swanton, 2001): determination of the critical crop weed competition
period; and, evaluation of the threshold above which weed infestation becomes
19
detrimental to the crop. Hall et al. (1992) defined the 3-leaf and 14-leaf stages of plant
development as the critical period for weed control in maize.
Aflakpui et al. (2005) stated that weeds have a competitive ability over young maize
seedlings and therefore it is necessary to keep fields free from weeds at least in the first
4-6 weeks after sowing. The need to control weeds during the early stages of the crop is
known to be critical (Evans et al., 2003).
The effect of weeds is so devastating that Vengris (1995) in an experiment on plant
nutrient competitions between weeds and corn, concluded that even at high rate of
nitrogen, potassium and phosphorus, the growth and yields of maize were reduced by
weeds; and apparently it is not practical to attempt to secure high yield of maize with
weed competition through heavy application of fertilizer.
2.5 Effects of Weeds on Maize Production
Weeds are objectionable to humans primarily because they reduce the quality and
quantity of agricultural production, and produce allergens or contact dermatitis that affect
public health (Ware and Whitacre, 2004). (Zimdahl, 1983) indicated that weeds and poor
soil fertility are big constraints for African smallholders.
Chikoye et al. (2005) attributed maize yield losses ranging from 50% to 90% to weed
competition. They noted that manual weeding is the predominant method of control used
by smallholder farms in Africa. However, this method is time-consuming, laborious, and
very expensive, whereas herbicides were shown to improve yield. Annual weeds can
20
reduce yield and quality of corn, with yield losses of 10 to 35% where weeds are not
controlled (Young et al., 1984).
Weeds are different from the other pests that pose problems in crop production in that
they are relatively constant, whereas outbreaks of insects and disease pathogens are
sporadic (Gianessi and Sankula, 2003). Apart from the quantitative damages caused by
weeds due to competition with water, light and nutrients (Coble et al., 1978; Coble et
al.,1981; Jordan et al., 1987) and to the antagonism (parasitism and allelopathy), weeds
are able to cause qualitative indirect damages due to cereal yield reduction,
contamination of seeds (Anderson, 1983), slowing of tillage and harvesting practices.
Clark et al. (1998) looked at corn production in California and concluded that weed
damage was more of a problem than losses from pests and diseases.
Koch (1992) estimated that the amount of food lost through weed competition, despite
weed control, was 25% of potential production in developing countries, and was one of
the major labour-consuming operations in traditional crop production, amounting to 30 70% of the total labour input. Porwal (2002) summed up with the comments that severe
infestation of weeds particularly in early stage of crop establishment ultimately accounts
for a yield reduction of 40% and that farmers’ practice of manual hoeing is costly, time
consuming and back breaking, particularly in heavy soils. Yield losses attributed to
unchecked weed growth throughout the crop life cycle in corn has been estimated at
about 50 to 87% (Magani, 1990).
21
2.6 The Benefits of Herbicide Use in Maize Production
Herbicides are one of the crucial factors in a worldwide increase in cereal production.
Herbicides contribute effectively and profitably to weed control, environmental
protection, and, in the same time, saving labour necessary for weed control practices,
reduced soil erosion, saved energy, increased maize production, reduced the cost of
cereal farming. Therefore, herbicides benefit society as a whole.
The importance of herbicides in modern weed management in maize production is
underscored by estimates that losses in the agricultural sector would increase about 500%
without the use of herbicides (Bridges 1992; 1994). Nowadays,maize production is facing
a difficult situation. The world population is rapidly increasing (over 6 billion inhabitants
on Earth surface now and estimated 9 billion in 2050) (Berca, 2004), every day
decreasing the arable surface (nearly 2 billion hectares worldwide have been degraded
since mid of the previous century) [Scherr and Yadav, 1996].However, there is lack of
knowledge, delusions, and controversy in the world about herbicides use and its potential
benefits for world food production.
Clearly the farmer using herbicides in maize production is saving money or effort on
mechanical weed control costs – a direct benefit to him. But there is an environmental
benefit too in reduced use of fossil fuels and reduced soil disturbance in no-till systems –
representing a common good benefit to us all. Beneficiaries may be individual farmers,
farming
communities,
businesses,
regulatory
populations or the whole living world.
22
authorities,
researchers,
national
Herbicides in maize production may bring benefits in a range of different areas, including
financial (saving money because labour is expensive), physical (reducing drudgery of
workers doing manual weeding), environmental (less use of fossil fuels in powered
machinery, controlling weeds without disturbing the soil) and social (reduced drudgery,
improvement of the living environment on public and personal-use amenity). Herbicides
were shown to be effective in trials but are said to have much more potential for
increased use by cereal farmers (Zvonko, 2007).
2.6.1 Herbicides protect environment
The increasing production and use of the new “low-rate” and “environment-friendly”
herbicides for maize production has reduced the risks for non-target organisms and the
environment as a whole. Herbicides use in corn declined by 23000 tons, largely due to
the replacement of the older high rate herbicides (e.g. cyanazine, metolachlor, EPTC)
with new low-rate herbicides (e.g. flufenacet, mesotrione, rimsulfuron, nicosulfuron).
The new weed management technology based on environmental principles use
“environment-friendly” herbicides, mainly glyphosate and glufosinate. These herbicides
have little residual activity, are low in mammalian toxicity, and have an average half-life
in soil of about 40-60 days. This means little restriction for crop rotation and low
environmental degradation (Pacanoski, 2006). Also, the price of glyphosate declined by
16% between 2001 and 2005 (Salassi and Breauh, 2005). Because of these characteristics
glyphosate and glufosinate are the most sold out farm products in the world (Dinham,
2005).
23
2.6.2 Herbicides save labour for weed control
Use of herbicides for weed control reduces hand labour requirements for many maize
production activities, which has become scarce and expensive in many parts of the world
(Zvonko, 2007). The author noted that in 1830, four farmers supported five non farmers,
but one-hundred years later, in 1930, subsistence ratio was 1 to 10.Removing weeds
manually is very labour-intensive (Riches et al., 2005) and therefore expensive. Using
herbicides to reduce the drudgery of persistent weeding, makes a lot of sense, especially
in cases of chronic labour shortages. Herbicides also reduce seasonal variation in labour
markets and the total labour needed for hand weeding, stabilizing labour requirements
and freeing workers to pursue higher-value opportunities.
Takeshita and Noritake (2001) reported that farmers in Japan used to spend 50 hours to
weed 0.1 ha by hand. In reality, a farmer used to spend 6-7 days per 0.1 ha for weed
control (before herbicides). The same problems with manual weeding apply elsewhere.
An estimated 70 million additional workers would be required in the US alone if handweeding was the only option (Anon, 2003). Also weeding is not a popular job so people
are not always willing to do it.
Mechanical weeding is difficult in many crops and in some parts of the world neither the
motive power nor the machinery is available. Herbicides overcome many of these
problems because they control weeds in a way that is quicker and easier than mechanical
methods and usually requires far less manpower. The heavy labour demand of weeding in
maize was emphasized by Parker and Vernon (1982) frequently contributing to a labour
bottleneck early in the rainy season when other crops are also being planted and weeded.
24
Delaying weeding to spread the labour loads led to yield losses, while delaying some of
the planting also reduced the potential yield of the crop (Parker and Vernon, 1982).
Chikoye et al. (2004) reported that weeds and shortage of labour for their removal are
two of the most important production constraints in smallholder farms and smallholder
farmers spend 50-70% of their total available farm labour on weed control by hoeweeding maize fields. In replicated trials in the first season, herbicide use gave an 11%
yield advantage over traditional cultivation and saved 16 man-hours/ha or 80% of the
labour normally used for weeding (Jennings and Drennan, 1979). The authors stated that
crops that have high labour requirements for weeding were becoming more difficult to
grow unless herbicide was used. Mohammad and Noor-ul (2004) reported that because of
acute shortage of labour and frequent monsoon rains, during the early growth period of
maize, hand weeding or mechanical weeding operations are usually delayed or left
altogether. In such situations, herbicides offer the most practical, effective and
economical method of weed control and increase crop yield.
2.6.3 Herbicides save cropland of erosion
Escalating land degradation threatens crop and pasture land throughout the world (Lal
and Pierce, 1991; Pimentel et al., 1995). The major types of degradation include water
and wind erosion (Pimentel et al., 1995). Worldwide, more than 10 million hectares of
productive arable land are severely degraded and abandoned each year (Houghton, 1994;
Pimentel et al., 1995). Agricultural erosion by wind and water is the most serious cause
of soil loss and degradation. Soil erosion on cropland ranges from about 13 tons per
25
hectare per year (t/ha/yr) in the United States to 40 t ha-1 yr-1 in China (USDA, 1994;
Wen, 1993; McLaughlin, 1993). Worldwide, soil erosion averages approximately 30
t/ha/yr, or about 30-times faster than the replacement rate (Pimentel et al., 1995). Erosion
adversely affects maize crop productivity by reducing the water-holding capacity of the
soil, water availability, nutrient levels and organic matter in the soil, and soil depth
(Pimentel et al., 1995).
Elimination of tillage means that the growers must rely entirely on herbicides to control
weeds (Triplett and Doren, 1977; Triplett, 1985). Otherwise, without herbicides growers
could no longer practice no-till agriculture, which means that erosion would have
increased by 152 million tons in 2001 and 178 million tons in 2005 (USDA, 2006).
Croplife (2004) also reported that no-till systems involving herbicides increased maize
yields by 45% in a normal year in Uganda, and by 48% in a dry year.
2.6.4 Herbicides control difficult or dangerous weeds
Controls of noxious, difficult and parasitic weeds are special examples in which
herbicides can have an important role in maize production. Yoldwasser et al. (2003)
found in a study in Israel that efficient, selective, low cost and easy to apply herbicides
can be used for control of the parasitic weed Orobanche. Chikoye et al. (2002) reported
that spear grass is a noxious weed widespread in most tropical zones of the world. Their
studies in West Africa in maize and cassava to examine different tactics for control
showed that plots that received glyphosate or those weeded five times had 28–59%
26
higher crop yields than plots weeded twice at all locations. It was cheaper to use
glyphosate than hand weeding for spear grass control in both crops.
Darkwa et al. (2001) worked with two grass weeds, Cyperus rotundus and Imperata
cylindrica that prevent potential maize yields being reached in Ghana. Trials showed that
tuber populations of C. rotundus could be reduced by 95% after glyphosate application at
1.8 kg a.i. /ha. Lum et al. (2005) reported that Cogon grass, an aggressive perennial
weed, causes severe yield losses up to 50% in major crops of the moist savannah of West
Africa. Management options commonly used by small farmers to control Cogon grass are
slashing, hand-weeding, burning, deep tillage, use of cover crops, and herbicides. Handweeding and hoe-tillage are very popular but use up lots of labour and are not effective
on underground rhizomes (Lum et al., 2005).
2.6.5 Herbicides save energy
The use of low-rate herbicides is decreasing the energy investment in each herbicide
application. Precisely, the amount of fuel used per acre for a herbicide application is
estimated at 0.42 litres, while the amount of fuel used to cultivate an acre is estimated at
1.7 litres (Williams and Selley, 2005). According these authors, the total number of
herbicide applications currently made on treated acres is 367 million, which implies the
use of 151 million litres of fuel for herbicide application. The total number of cultivations
that would be made as replacement for herbicides is estimated at 838 million, which
implies the use of 1.43 billion litres for cultivation. The use of herbicides rather than
cultivation would result in an aggregate reduction of 1.28 billion litres fuel annually.
27
If consideration is given to the fact that fuel costs continue to increase, the energy
benefits of herbicides use should continue to increase, as well (Svensson, 1982). Semb et
al. (2003) reported that all weed control practices (including herbicides especially) return
a high energy output in relation to the input because of the tremendous increase in crop
yields when weeds are controlled. They found that economic returns from herbicide use
were very positive too.
2.6.6 Herbicides protect and increase maize production
Herbicides help to maintain high and stable world-wide yields and prevention of world
wide hunger (Gianessi and Sankula, 2003). According to a series of studies conducted by
USDA, WSSA and AFBF, crop yield losses were estimated at 5-67%, depending on the
crop species, if no herbicides were used (Gianessi and Sankula, 2003). Bigler et al.
(1992) reported that weed control in cereals is accomplished almost exclusively by
herbicides in Europe, where 11% of the world cereal production is grown on only 6% of
the world’s cereal acreage, indicating highly intensive production.
Balsari (1993) compared mechanical weed control with herbicides in the Netherlands on
maize over several years. In maize, mechanical weed control was 25% to 44% less
effective than that obtained with herbicides and gave a yield reduction from 6% to 18%.
Becker and Staniforth (1981) obtained higher yield in maize with weedicides than with
cultural weed control method. Jehangeri et al. (1984) reported that application of
selective herbicides provided 65 to 90% weed control and 100 to 150% more maize
yields than unweeded control. Kibata (2002) reported that herbicides used in two crops in
28
Kenya improved the economic yield and help in particular when labour is short for
weeding at critical times. Yields increased dramatically (94% in beans and 53% in maize)
when herbicides were applied.
Yadav (2003) reported that traditional methods of hand weeding and hoeing, in addition
to being expensive and time consuming were ineffective in controlling the weeds as new
weed seeds germinated after every hoeing and re-infested the crop. Moreover, hoeing is
not possible during the rainy season and labour shortage at that time further accentuates
the problem. Under these situations, chemical and/or integrated methods of weed
management are the only viable and feasible alternative. They reported that usage of preemergence herbicide proved best, reducing the dry weight of weeds by 80 to 88%.
Zanin et al. (1994) calculated the cost-benefit thresholds for chemical weed control in
North-Central Italy and herbicide use always had a probability of positive net return of
>80% for wheat, maize, and soybeans and >95% for sugar beets. Schroder et al. (1984)
reported that increased use of herbicides accounted for 20% of the increase in corn yields
during the period 1964-1979 in the USA. Prematilake et al. (2004) reported that in Sri
Lanka weed control with herbicides was superior to that of hand weeding. Manual weed
control was less efficient and its cost was ever increasing.
2.7 The Use of Lower Doses of Herbicides
An enormous increase in public concern for the protection of the environment and
increased awareness of pesticide residues in food and water, have necessitated intensive
studies into the possibilities to reduce the herbicide use in maize production. Herbicides
29
are used in combinations to broaden the spectrum of weeds controlled by a given
herbicide application and to reduce the dose of each components of the mixture applied
per unit area i.e. low concentrations of the herbicides can be used (Akobundu, 2000).
Many farmers often search for information on methods for weed suppression with
lowered herbicide doses. In literature, we can find interesting information on possibilities
of drastic reduction of herbicide doses without causing the significant increase in maize
yield losses. Most reports present cognitions that doses of herbicide can be lowered by 15
to 30% without a significant impact on yield loss in situations with moderate weed
pressure and when at least one mechanical weed control treatment in season is carried out
(Rola et al., 1999; Schans and Weide, 2000).
The herbicide doses and efficiencies that are needed for successful suppression of weeds
and prevention of yield loss differ significantly and depend a lot on the composition of
weed population and specific local stand conditions. In dense maize stands with moderate
weed pressure, many times farmers do not need to apply 100% doses of herbicides to
hold the weed population below a threshold limit (Lešnik, 2003). It is difficult to
determine exactly the rate to which the herbicide dose could be lowered in each specific
situation in each specific field. Intensive research is carried out on modelling the
interactions between weed density, crop density, reduced herbicide doses and yield loss.
Best results were achieved in cereals (Kim et al., 2002).
Usually it is concluded that further reduction of herbicide doses can be achieved by
banded application and intensification of mechanical weeding. Lešnik, (2003) agreed
30
with that, but asserted that it is well known that intensive mechanical weeding using
machines also has many ecological disadvantages (greater consumption of petroleum,
greater CO2 emissions, greater soil compaction, bear soil effects, acceleration of nutrient
leaching). Simple replacement of herbicide use with many mechanical cultivations is not
the best solution, because farmers only replace some ecological benefits (less herbicides
in soil and in water) with some ecological disadvantages, without having a noticeable
economic benefit (Lešnik, 2003).
Some authors have also established that greater reductions of herbicide doses (50–70%)
can provide satisfactory weed control and good economic return in suitable conditions
(Forcella, 1995; Schans and Weide, 2000). A few experiments revealed possibilities of
80% (Alm et al., 2000), or even 90% (Weide et al., 1995) of herbicide dose reduction
without risk for significant increase in yield loses.
2.8 Composition, Characteristics and Efficacy of Lumax
Lumax is the brand name of a selective corn herbicide that is manufactured by Syngenta
(Wikipedia, 2009).The active ingredients of Lumax are S-metolachlor (29.40%), Atrazine
(11.00%), Mesotrione (2.94%) and other ingredients (56.66%). Per gallon, its active
ingredients are S-metolachlor (2.68 pounds 1.22kg), Mesotrione (0.268 pounds
0.122kg),and Atrazine (1.0 pound 0.454kg) (Syngenta, 2009). Armbrust et al. (2007)
noted that Lumax is a premix of mesotrione (Callisto), s-metolachlor (Dual II Magnum),
atrazine and a safener benoxacor.
31
Lumax is a suspoemulsion (SE) (Syngenta, 2009). A suspoemulsion system consists of
solid particles and oil droplets suspended in a continuous aqueous phase. Lumax utilizes
the proven corn safener, benoxacor, to ensure crop safety even in adverse weather
conditions. Syngenta (2009) pointed out that water quality and temperature may affect resuspension and Lumax may require compatibility agents.
Based on its site of action and inury symptons, Lumax is classified as an inhibitor of the
enzyme p-hydroxyphenylpyruvate dioxygenase (Hartzler, 2009). Lumax provides highperformance, broad-spectrum control of the toughest grasses and broadleaf weeds in corn
including waterhemp, velvetleaf, lambsquarters and pigweeds (Syngenta, 2009).
According to the manufacturers, Lumax® herbicide controls weeds with three different
modes of action. Mesotrione, the broadleaf weed control component in Lumax, the same
active ingredient that powers Callisto® herbicide, is readily taken up by the roots and
shoots of the plant and then rapidly translocated throughout the plant via both xylem and
phloem. Uptake of the two remaining ingredients occurs readily through the roots and/or
shoots of germinating seedlings and then moves in the xylem. Utilizing three different
modes of action, Lumax is a comprehensive tool for managing against herbicide
resistance (Syngenta, 2009). Lumax, which is powered by the Callisto® chemistry, owes
its origins to the discovery of a natural herbicide secreted by the Callistemon plant. This
is Callisto Plant Technology® and it brings unprecedented broadleaf weed control and
exceptional crop safety to Lumax that the competition cannot match (Syngenta, 2009).
Lumax® herbicide may be applied to field corn from 14 days preplant through 12-inch
32
tall corn. Lumax will not provide consistent control of grasses if applied after the weeds
have emerged.
Early-season weed control is absolutely critical to achieving full yield potential. Syngenta
(2009) noted that Lumax offers unprecedented broadleaf weed and grass control that
keeps fields clean early in the season. And, its high-performance residual activity
manages weeds through crop canopy. Weed emergence patterns change from year to
year, and some weeds exhibit continuous emergence throughout the growing season.
Syngenta (2009) emphasized that Lumax delivers long-lasting residual control for six
weeks or more, which makes it a perfect fit for use in both conventional and glyphosatetolerant corn. Similarly, Syngenta (2005) reported that research proves that early season
weed control leads to higher corn yields. So, Lumax® herbicide, an early corn herbicide
is specifically formulated to block out weeds from pre-plant all the way through canopy
with longer residual control of broadleaf weeds and grasses than any single-chemistry
alternative, including Harness® Xtra, Keystone® and Guardsman Max®.
Crop injury can negatively impact yield, so it is important to choose a herbicide that not
only controls weeds, but also has excellent crop safety. Lumax had the lowest average
crop injury and had no locations with greater than 10 percent injury. It is not surprising
that in rare cases conditions may be right to produce a negative crop response. However,
Armbrust et al. (2007) observed that Lumax is typically very safe on corn. In research
conducted at Purdue University, studies that collected injury responses reported no more
than 8% bleaching and 3% leaf malformation, often not significantly different than the
check (Armbrust et al., 2007).
33
The findings in 21 university trials conducted across the Corn Belt in 2004 (Syngenta,
2005) indicated that Lumax provided the best overall weed control (92 percent control on
average across all grass and broadleaf weeds tested). The competitive products exhibited
overall weed control no higher than 87 percent. All products were applied at
recommended rates for the soil type at each site (Syngenta, 2005). Furthermore, when
compared to other conventional herbicide programs, Lumax supported higher yields by
providing better management of weed competition and excellent crop safety.
By using a one-pass, pre-emergence application of Lumax, across 21 university trials
conducted in 2004, Lumax produced a higher yield than all of these competitors,
averaging more than 171 bu./A. The average yield for Lumax was at least two bushels
higher and as much as 12 bushels higher than the competitors tested (Syngenta, 2005).
Lumax also offers superior application flexibility, from pre-plant through early postemergence. And, with three distinct modes of action, Lumax is a Resistance Fighter®
brand. This means Lumax is in the battle against resistance to glyphosate, triazine and
ALS chemistries (Syngenta, 2005).
A pre-emergence application of Lumax consistently provides the opportunity to achieve
one-pass weed management and maximum yield potential by providing season-long,
broad-spectrum weed control. In most cases, Lumax should be applied at 3.0 qts/A. In
soils less than three percent organic matter, Lumax may be applied at 2.5 qts/A
(Syngenta, 2009).
Hager and Sprague (2007) stated that Lumax is a recently registered premixture
containing 2.68 pounds of active ingredient per gallon of S-metolachlor (Dual II
34
Magnum), 0.268 pound of active ingredient per gallon of mesotrione (Callisto), and 1.0
pound of active ingredient per gallon of atrazine. Lumax is a selective preemergence
herbicide that controls annual grasses, annual broadleaf weeds, and sedges in field, seed,
and silage corn. Lumax may be applied up to 10 days before planting (EPP), PRE, and
EPOS up to corn 5 inches in height. Application rates range from 2.5 to 3.0 quarts per
acre depending on soil texture and soil organic matter content. A typical use rate of 3.0
quarts per acre of Lumax is equivalent to applying 2 pints of Dual II Magnum, 6.4 fluid
ounces of Callisto, and 0.75 pound of active ingredient per acre of atrazine ( Hager and
Sprague, 2007).
Chikoye et al. (2009) studied the efficacy of various herbicides against weeds of maize in
field trials at Ibadan, Nigeria in 2003 and 2004. The formulations were atrazine
(Gesaprim® 90 WDG at 3.5 kg a.i. ha-1 and Rhonazine® 80 WP at 3.0 kg a.i. ha-1), a
mixture of atrazine and metolachlor (Primextra® Gold™ 660 SC at 4.0 kg a.i. ha-1 and
Primextra® 500 FW at 2.5 kg a.i. ha-1), and a mixture of mesotrione, S-metolachlor and
atrazine (Lumax® at five rates: 1.88-2.96 kg a.i. ha-1). Unweeded and hoe-weeded
treatments were controls. Lumax® at all rates, Rhonazine® at 3.0 kg a.i. ha-1, and
Primextra® at 2.5 kg a.i. ha-1 controlled sedges, Commelina benghalensis, and Pueraria
phaseoloides as effectively as the weeded control (95-100%). Weed density and biomass
were significantly reduced and maize yield increased by 12-22%. The highest yield was
in treatments with 2.15 - 2.96 kg a.i. ha-1 of Lumax® and 3.5 kg a.i. ha-1 of Gesaprim®,
and the weeded control. Lumax® was more effective for weed control at lower rates than
the previously used formulations (Chikoye et. al., 2009).
35
Wenzel (2002) reported that Syngenta claimed the potent combination of the unique
mesotrione chemistry including its formulation with atrazine and S-metolachlor, dubbed
Lumax herbicide, was designed for preemergence application on corn, and one
application provides season-long control of all major broadleaf and grass weeds . The
company supported its “season-long” by having some fields sprayed with Lumax near the
University of Wisconsin’s Arlington research farms. While the untreated check plots
were choked with foxtails and giant ragweed, the Lumax plots were relatively clean,
exceptionally good for only one herbicide treatment. There were very few escapes
(Wenzel, 2002). The author pointed out that despite heavy rains shortly after the crop
emerged, Lumax stayed put and did its job on the heavy Arlington Prairie soils. The
herbicide has an excellent crop safety profile, and the corn looked tall and healthy, and
was very good for both grain and silage hybrids (Wenzel, 2002). He noted that at
Arlington, the recommended rate of 3 qts./acre provided the best results, and lower rates
had correspondingly more escapes. Lighter soils might have achieved equitable results
with a lower 2 1/2-qt. rate, which the company recommends when soil organic matter is
less than 3%.
2.9 Effects of Herbicides on Maize Performance
2.9.1 Maize Emergence and Vegetative Growth
If there are any problems with corn emergence, herbicides are often blamed as the cause.
However, herbicides may or may not be the culprit. Boerboom (2004) gave a few points
that should be remembered if any emergence problems are encountered as follows:
36
First, corn must germinate before a herbicide can cause damage. This means that a
whole, unsprouted, dead kernel was not killed by a herbicide. However, if the kernel has
a radicle or sprout, then there is potential for herbicide uptake and damage.
Next, the modes of action of the herbicides and the potential for injury need to
considered. For instance, there are three herbicide modes of action that require light for
activity such as the photosynthetic inhibitors (i.e. atrazine, Princep, Sencor), pigment
inhibitors (i.e. Balance, Callisto, which is in Lumax and Camix, Command carryover),
and PPO inhibitors (such as with Flexstar carryover). These herbicides will not damage
the tissue of a seedling while it is underground and protected from sunlight. As seedlings
emerge and are exposed to light, these herbicides can then cause damage.
Boerboom (2004) suggested that other reasons for injury such as seedling disease, insect
damage, soil crusting, fertilizer burn, frost, etc. still need to be considered as potential
reasons for poor corn emergence or growth. Herbicides are not the only reason for poor
corn emergence or growth. Maize can be damaged by the improper use of agricultural
chemicals such as herbicides, fertilizers, or insecticides. The damage is usually the result
of applying the chemical carelessly, at too high a rate, at the wrong growth stage, or when
the plants are under drought or temperature stress. Usually problems of chemical injury
are the result of occasional accidents and are not major limitations to yield in an area, but
it is important that these problems are recognized.
Herbicide injury to maize may occur if the product is not approved for use on maize; the
application rate of the product was too high or product application overlapped; timing of
37
application was incorrect and/ or a nonselective herbicide was applied with no shield or
with a shield which did not work. The damage could also be due to drift from adjacent
fields (Madison, 2009).
In rare cases, corn seedlings may fail to emerge from the soil and "leaf out" underground
as a result of injury from these herbicides. Corn that has emerged and has been injured as
a result of one of these herbicides will appear malformed and have twisted leaves that do
not unroll properly. This is often referred to as "buggy-whipping" (Bradley, 2005).
Fortunately, this injury is usually short-lived and rarely causes yield reductions. Most
plants that have been injured as a result of these herbicides will grow out of this injury
once soil drying occurs. Johnson (2005) found 17% stunting with a spring application of
Lumax at 3 qt/A on a sandy soil. Johnson (2005) indicated that the corn recovered and no
injury was observed by 6 weeks after treatment.
Obviously, plant stand and grain yield would be reduced if some of the plants die.
Moreover, optimum number of plants is an important factor for controlling weeds and
increased yield. It would be logical to expect that weed management should improve if
the optimum maize population is maintained (Nawab et al., 1997).
Owen (2002) reported that many of the herbicide applications were made during weather
conditions that likely resulted in stressed corn. Corn that is stressed by weather or other
factors is unable to metabolize herbicides as rapidly as vigorous corn, thus the herbicide
accumulates at relatively high concentrations. When weather turned favourable, the corn
began to grow rapidly and because of the relatively high dose of Callisto in the plant,
injury developed (Owen, 2002). Other stresses attributable to other herbicides (such as
38
ALS inhibitors or plant growth regulators), diseases, or compaction enhanced the injury
from Callisto by further limiting herbicide metabolism. The injury appeared within a
couple of days of Callisto application. Although striking in appearance, the overall
impact of the Callisto injury on corn was minimal. New growth did not demonstrate
injury and the affected fields appeared to be recovering (Owen, 2002).
In an evaluation of the effect of three doses of pre- emergence (Harness xtra at 0.5, 2.0,
2.5 l/ha) and three doses of post- emergence (atrazine at 0.5, 1.0, 1.5 l/ha) herbicides
applied and studied in comparison with hand weeding and weedy check on maize crop,
Ali et al. (2003) reported that minimum number of days to emergence (7.33 days) were
recorded at 2.0 l Harness xtra /ha. In mean values for pre- emergence herbicides vs postemergence herbicides (Harness xtra compared with atrazine), pre- emergence herbicides
resulted minimum number of days as compared to post- emergence herbicides. Ali et al.
(2003) opined that it may be due to less competition between maize seeds and weed seeds
for available space, moisture and nutrients in the plots treated earlier with pre- emergence
herbicides. For phytotoxicity of herbicides on crop, each treatment was observed
thoroughly but no such effect was noticed during the course of the study (Ali et al.,
2003).
Herbicide injury can be distinguished from foliar disease by looking for burning which
occurs in patterns from the sprayer nozzle and which only affects leaves of a certain age
which were exposed when the chemical was applied (Madison, 2009). If a misapplication
of a growth regulator herbicide has occurred prior to planting, corn plants can leaf out
underground or show symptoms very similar to the chloroacetamide herbicides. Usually
39
this type of injury is due to the planting slot not being properly closed and/or corn being
planted too shallow. Each of these scenarios most often causes the herbicide to come into
direct contact with the germinating corn seed.
Application of a good contact or systemic herbicide prior to planting will ensure that
maize field is free from weeds during the critical growth stage of the crop; that is up to
about four weeks after planting (Bradley et al., 2000). Evaluations were made at 7 and 18
days after treatment for numbers of injured plants as well as the amount of the plant
expressing the injury. Jemison and Wilson (2002) saw no injury to any variety when
mesotrione (Camix or Lumax) was applied preemergence. Injury from Lumax or Camix
was negligible. There was significant injury to sweet corn from some of the
postemergence treatments.
The height of plant is an important growth character directly linked with the productive
potential of plant in terms of fodder, gains and fruit yield. An optimum plant height is
claimed to be positively correlated with productivity of plant (Saeed et al., 2001). Higher
weed densities compete with maize for nutrients, soil moisture, light and carbon dioxide
and considerably reduce plant growth including plant height (Hussain, 1983; CRI, 1996).
Similarly, it was reported that taller maize plants were produced by higher rates of Atoll
than lower rates at Orin-Ekiti in Nigeria (Makinde and Ogunbodede, 2007).
From another dimension to the discourse on data concerning plant height of maize
subjected to different methods of weed control, plant height was not significantly affected
by various herbicide treatments (Subhan et al., 2007). Subhan et al.(2007) reported that
although not approaching the level of statistical significance, the taller plants (163, 160,
40
160 cm) were attained in the plots treated with Dual gold, Primextra gold and Atrazine
when applied as pre-emergence, while minimum plant height of 132 cm was recorded in
weedy check plots. These results (Subhan et al. 2007) are in agreement with Sakhunkhu
and Faungfupong (1985), who also reported that weed control methods had no effect on
plant height of maize.
Riaz et al. (2007) found that plant height of maize as affected by study years were
statistically non-significant. On the other hand, all weed control methods showed
significant effect on plant height of maize. The maximum plant height was observed with
Chemical Weeding at 2-3 leaf stage of weeds + Hand Weeding at 50 DAS and
Mechanical Weeding at 20 DAS + Hand Weeding at 50 DAS. Ahmad et al. (1988),
Behera and Singh (1998) and Williams et al. (1998) have reported similar results
obtained from various weed control techniques.
Application of all herbicide treatments significantly produced taller plants at 6 and 9WAS
than the weedy check (Gana et al., 2008). Among the herbicide treatments, application
of metolachlor at 2.0 and its combination with atrazine at 1.0 + 1.0 and 1.25 +
1.25kga.1/ha in both years significantly produced taller plants and higher popcorn grain
yield (kg/ha). With one supplementary hoe-weeding at 7WAS the effectiveness of
herbicide treatments improved popcorn growth parameter (height) (Gana et al., 2008).
This confirms herbicide as a substitute for hoe-weeding especially where labour is
limiting and land is large (Akobundu, 1987).
41
2.9.2 Maize Phenology
Nawab et al. (1997) reported that number of days to tasselling was increased in weed free
plots as compared to check plots. Subhan et al. (2007) reported that days to 50% silking
in maize were non-significant statistically. However, overall Subhan et al. (2007)
observed that plots treated with weed control methods took more days to silking than no
weeding. The findings of Subhan et al. (2007) were in agreement with Nawab et al.
(1997), who reported that number of days to tasseling was increased in weed-free plots as
compared to check plots.
Subhan et al. (2007) reported that weed control treatments also showed non-significant
effects. However, on average the maximum days to maturity were recorded in plots
treated with weedicides as compared to hand weeding and no weeding (Subhan et al.,
2007). The findings of Subhan et al. confirmed that of Nawab et al. (1997), who reported
that days to maturity were increased in weed free plots as compared to check plots.
Comparing the results, Primextra gold (pre-em) plots took more days to maturity as
compared to other treated plots (Subhan et al., 2007).
2.9.3 Maize Yield and Yield Components
Riaz et al. (2007) reported that, between study years, a significant difference in grain
yields of maize was observed being maximum in second year. To Riaz et al,this might be
due to minimum weed seed bank and eradication of weeds providing healthy
environment for crop plant growth during the second year. A significant effect of
different weed control methods was observed on grain yield of maize during both years
of study. Among various weed control methods, Chemical Weeding at 2-3 leaf stage of
42
weeds + Hand Weeding at 50 DAS showed promising results during both years of study.
A 34% increase in grain yield of maize was observed due to effective weeding by this
treatment (Chemical Weeding at 2-3 leaf stage of weeds + Hand Weeding at 50 DAS )
followed by about 33% increase in grain yield with Mechanical Weeding at 20 DAS +
Hand Weeding at 50 DAS and about 32% increase with WC2 as compared to Weedy
Check. Jehangeri et al. (1984) reported that application of selective herbicides provided
65 to 90% weed control and 100 to 150% more grain yield of maize than un-weeded
control. They further demonstrated that chemical method of weed control in maize was
more effective than the mechanical one.
Chikoye et al. (2006) reported that maize grain yield from the hoe-weeded control was
among the highest, because of good weed controlas well as low weed dry matter in hoeweeded plots. However, hoe-weeding is very tedious, time consuming and takes up a
significant proportion (about 50 to 80%) of the total labour budget (Chikoye et al., 2002).
Also, labour is scarce, during the early stages of crop growth when it is necessary for
weeds to be controlled, thus making this management option more expensive for
resource-poor farmers (Chikoye et al., 2002). Untimely weeding causes significant crop
losses (Chikoye et al., 2004). The maize grain yield in most plots that received herbicide
was better than that in the untreated plot because of good weed control. The negative
relationship between grain yield and weed dry matter supports this observation (Chikoye
et al., 2006).
43
Gana et al. (2008) reported that metolachlor at 2.0 and its combination with atrazine at
1.0 and 1.25 + 1.25kg a.i/ha gave the best weed control and grain yield comparable to the
hoe-weeded control and therefore recommended it for weed control in pop-corn for
farmers in the Northern Guinea Savannah of Nigeria.
Chikoye et al. (2004) indicated that maize grain yield was significantly higher in the
treatment in which either the herbicide mixture or velvetbean was combined with 40,000
maize plants ha−1 and weeded thrice. Chikoye et al.(2004) stated that the lowest maize
grain yield was obtained with the farmer's control. Weed dry matter was 60% more in the
farmer's control than in velvetbean combined with 40,000 maize plants ha−1 and weeded
three times. The authors recommended that herbicide or velvetbean in combination with
medium maize density and weeding three times (2, 4, and 6 WAP) for weed management
in the northern Guinea savanna.
Chemical weed control gave the highest grain yield, but it was not significantly different
from either the hand hoe system or treatments of animal drawn cultivators when
supplemented by the hand hoe or herbicide (Miller et al., 1980). The authors suggested,
to improve further weed suppression and crop yields, animal drawn cultivators should be
combined with herbicide or hand hoe.
Subhan et al. (2007) observed significant differences in grain yield due to weed control
treatments. Subhan et al. (2007) reported that weed control treated plots produced
maximum grain yield and results were in agreement with Saini (2000), who reported that
weed control treated plots showed increased yield. Subhan et al. (2007) noted that the
44
pre-emergence herbicides produced higher grain yield. The possible explanation the
authors gave for the increase in grain yield was that weed control by different methods in
the study diverted the nutrients to the crop, which in turn resulted in increased grain
yield. These results of Subhan et al. (2007) confirmed those of Ali et al. (2003) and Khan
and Haq (2004).
Riaz et al. (2007) revealed that 1000- grain weight was significantly affected by different
weed control treatments being maximum with Chemical Weeding at 2-3 leaf stage of
weeds + Hand Weeding at 50 DAS closely followed by Mechanical Weeding at 20 DAS
+ Hand Weeding at 50 DAS and Hand Weeding at 20 and 40 DAS. Riaz et al. (2007)
were of the opinion that this increase in 1000-grain weight was possibly due to effective
weed control, which resulted in healthy crop stand and ultimately higher grain weight.
These results got support from the previous findings of Ahmad et al. (1988). Kandasamy
and Chandrasekhar (1998) reported that the traditional (non-chemical) method of weed
control effectively minimized weed competition and maximized maize yield.
Subhan et al. (2007) reported that different herbicides at different application times had
significant (P<0.05) effect on the 1000 kernel weight. Also, Subhan et al. (2007)
indicated that maximum 1000 grain weight (133 g) was produced by Primextra gold (preem) which was also found statistically at par with Dual gold. Minimum 1000 kernel
weight (109 g) was obtained in the weedy check. Subhan et al. (2007) attributed the best
performance of Primextra gold and Dual gold to the best weed control. Similar results
have been reported by Veseloskii (1993).
45
Riaz et al. (2007) reported that statistically non-significant difference was observed in
stover/stalk yield of maize crop between study years. On the other hand all the weed
control treatments showed statistically similar results with the exception of Mechanical
Weeding at 20 DAS. The lower yield in case of Mechanical Weeding at 20 DAS was due
to inadequate weeding as discussed by Pizzi et al. (1996). The treatment Chemical
Weeding at 2-3 leaf stage of weeds + Hand Weeding at 50 DAS out yielded among all
the weed control treatments that were approximately 33% higher as compared to control
(weedy check) treatment. The treatments Mechanical Weeding at 20 DAS + Hand
Weeding at 50 DAS and Hand Weeding at 20 and 40 DAS were next to Chemical
Weeding at 2-3 leaf stage of weeds + Hand Weeding at 50 DAS. Both of these treatments
(Mechanical Weeding at 20 DAS + Hand Weeding at 50 DAS & Hand Weeding at 20
and 40 DAS) caused increase in stalk yield of maize over control (weedy check)
treatment. These results (Riaz et al., 2007) were in line of those reported by Ahmad et al.
(1988) and Kandasamy and Chandrasekhar (1998).
Riaz et al. (2007) reported a significant difference in % harvest index of maize for two
study years with the maximum being during the second year. Riaz et al. (2007) explained
that this was probably due to adequate crop yield during the second year. The % values
for harvest index of maize crop as affected by different weed control methods showed
significant differences among the treatments during both study years. Riaz et al. (2007)
claimed that the increase in percentage of harvest index as compared to weedy check may
be attributed to adequate suppression of weed growth due to some residual effect as well
and more availability of plant nutrients to maize crop, which favoured better utilization of
46
photo-assimilates for grain yield formation. Similar results have also been discussed by
Ahmad et al. (1988).
2.10 Effects of Herbicides on Economic Benefits in Maize Production
In glufosinate-resistant maize, research studies indicate that the effects of weed
competition early in the life of the crop are such that pre-emergent herbicide application
as part of a spray programme still gives the best yield and economic return (Bradley et
al., 2000; Hamill et al., 2000).
Weed management in maize cropping systems has been studied in both sole cropping and
mixed cropping. Physical methods and chemical (herbicide) technologies, and cultural
(cover crops and intercropping) have been tried and were found to be successful
(Mwangi, 1999). However, analysis showed that the herbicide technologies were cost
effective and yielded higher returns than conventional methods (Muthamia, 1995).
Muthamia et al. (2001) reported that use of herbicides resulted in significantly higher
maize grain yields and economic benefits than hand weeding in sole maize crop. The
increase in yield was 25-50% with a mean of 33%, and economic benefits of 33% from
the use of herbicide weed management vis-à-vis hand-weeding in smallholder farm. Riaz
et al. (2007) reported that all the treatments gave higher net benefit as compared to
control (weedy check). The treatments (Chemical Weeding at 2 - 3 leaf stage of weeds +
Hand Weeding at 50 DAS) resulted in higher net benefit (Rs. 32060 ha-1). The treatment
(Mechanical Weeding at 20 DAS) had less net benefits (Rs. 29726 ha-1). But in case of
marginal analysis, Riaz et al. (2007) noted that Mechanical Weeding at 20 DAS was
found better than all the treatments with maximum marginal rate of return (688%). The
47
treatment (Hand Weeding at 20 and 40 DAS) was dominated due to less net benefit and
higher cost that varied, so it was uneconomical treatment at the prevailing crop and
herbicide prices. On the basis of their study Riaz et al. (2007) suggested that Chemical
Weeding at 2 - 3 leaf stage of weeds + Hand Weeding at 50 DAS or Mechanical Weeding
at 20 DAS may be used for controlling weeds in maize with fairly good economic
returns.
48
CHAPTER THREE
MATERIALS AND METHODS
3.1 Experimental Site/Location Description
The study was conducted at the Multipurpose Crop Nursery research field of the
University of Education, Winneba, College of Agriculture Education, Mampong-Ashanti
from September-December, 2009 and April-July, 2010. Mampong-Ashanti (7o45'N,
1o24'W) lies at an altitude of 402m above sea level and in the transitional agro-ecological
zone between the rain forest of the south and the Guinea Savanna of the north of Ghana.
The area experiences bimodal rainfall regime. The major rainy season begins from midMarch and ends in July. The minor season begins in August and ends in mid-November.
There is a dry spell of harmattan season from December to March. The annual average
temperature and rainfall figures are 30.8oC and 1094.2mm respectively (Asiedu et al.,
2001). The soil belongs to the Bediese series and it is deep, sandy – loam free from
stones, and red in colour. It is of the forest ochrosol type formed from voltaian sandstone
of the Afram plains with pH between 5.5 and 6.5 (Asiedu et al., 2001).
3.2 Experimental Design and Treatments
The experiment was laid out in a randomized complete block design with six treatments
and four replications. The six treatments comprised four rates of pre-emergence
application of Lumax 537.5 SE, hand weeding and weedy controls as follows:
49
(i)
Unweeded Control
(ii)
2l Lumax 537.5 SE/ha
(iii)
4l Lumax 537.5 SE/ha
(iv)
6l Lumax 537.5 SE/ha
(v)
8l Lumax 537.5 SE/ha
(vi)
Hoe-weeded check
The herbicide was applied using a CP15 knapsack sprayer calibrated to deliver 300l/ha
spray solution the same day as seeds were sown.
Plot size was 25.2m2 that comprised six rows, 75cm apart and 5.6m long. Paths of 1.0m
wide were left between plots and 1.5m between replicates.
3.3 Cultivation and Management Practices
3.3.1 Land Preparation
The land was cleared with cutlass and the stumps of the few available trees and shrubs
were removed with mattock. The land was disc-ploughed to the depth of about 8-10cm
and harrowed to give a fine tilth. Linning and pegging was done to mark out plots.
3.3.2 Planting/ Sowing
Seeds of the maize cultivar Akposoe were obtained from the Crops Research Institute,
Fumesua for planting. A germination test was conducted one week before planting to
determine the viability of the maize seeds and to prevent the problems arising from poor
stand. Three seeds per hill were sown on flat at a spacing of 75cm × 40cm at a depth of
50
3–5cm on 15th September, 2009 and 17th April, 2010 for the first and second seasons’
experiments, respectively. Seedlings were thinned to two per hill 10 days after sowing to
give a plant population of 168 per plot (66,666 plants per hectare).
3.3.3 Fertilization
A compound fertilizer, NPK (15-15-15) was applied as basal at the rate of 250kg/ha (i.e.
37.5kgN:P2O5:K2O/ha) by side placement at 10 days after sowing. Sulphate of ammonia
at 125kg/ha (i.e. 26.25kgN/ha) was top-dressed at five weeks after sowing.
3.4 Data Collected
3.4.1 Climatic Data Collected
Data on the amount of rainfall, maximum and minimum monthly temperature readings
and relative humidity during the cropping period were obtained from the Mampong
Meteorological Station at Ashanti Mampong.
3.4.2 Soil Preparation and Analysis
Soil samples were randomly collectedfrom0-20cm deep with a soil auger and bulked
together. A 50–gram composite sample was taken and analysed for physico-chemical
properties. Particle-size distribution was determined by the hydrometer method
(Bouyoucos, 1951). Soil pH was measured using the pH meter at 1:1 soil to water ratio.
The percentage organic carbon was determined by the Walkley Black wet oxidation
method (Walkley and Black, 1934) while percentage total nitrogen (N) was determined
by the micro-kjeldahl technique (Jackson, 1962). The present organic matter was
estimated by multiplying the percentage organic carbon by a factor of 1.724. The
51
exchangeable cations calcium, magnesium, potassium and sodium were determined by
using EDTA titration after extraction with 0.1N ammonium acetate at pH 7 (IITA, 1979).
3.4.3 Weeds Assessment
3.4.3.1 Weed Score
At two weeks after sowing maize, a meter square (1m2) was placed randomly at five
places within the four inner maize rows on each plot and marked out. Weeds within the
quadrat area were scored according to the scale used by Kombiok et al. (2003): 0 = not
weedy, 1 = moderately weedy, 2 = weedy, 3 = very weedy and 4 = highly weedy.
3.4.3.2 Weed Density
Weeds from two randomly sampled quadrat area per plot were carefully cut at ground
level, counts were made of the total number of weeds present in the 1m2 quadratand the
average determined for each treatment from 4 weeks after planting (WAP) and for every
fortnight till 12WAP.
3.4.3.3 Percentage Weed Control
From the weed counts at 6WAP, percentage weed control (PWC) per treatment was
estimated according to the formula used by Carson (1979):
52
3.4.3.4 Weed Flora
At 6WAP, the species of weeds harvested from each randomly sampled quadrat area per
plot were identified and counted. The weeds were then separated into grasses, broadleaf
weeds and sedges, and were counted according to their respective life form categories.
3.4.3.5 Weed Dry Matter
After each weed count at 6 and 12WAP in 2009, and from 4WAP and every 2 weeks up
to 12WAP in 2010, the harvested weeds were then put into brown paper envelopes and
oven dried at 75oC for 48h, and the average weed dry weight per treatment determined on
a sensitive scale (Methler PE 6000).
3.4.3.6 Weed Control Efficiency
At maize harvest, weed control efficiency (WCE) was calculated, using the weed dry
matter weight per treatment on the basis of formula by Patel et al. (2006) as:
.
where,
WCE = Weed Control Efficiency
DWC = Dry weight of weeds from control plot
DWT = Dry weight of weeds from treated plot
53
3.4.4 Vegetative Growth of Maize
3.4.4.1 Crop Establishment
Two weeks after sowing, seedlings from four middle rows per plot were counted and
their percentage establishment calculated. Crop injury effect from the various rates of
application of Lumax 537.5 SE was observed from seedling emergence to two weeks
after treatment (WAT).
3.4.4.2 Maize height
Maize height was determined at two weeks interval from 2WAP up to tasseling using ten
maize plants randomly selected from the four middle rows per plot. Maize height was
measured from the ground level of the stem to the base of the last emerged (flag) leaf
using a graduated height pole.
3.4.4.3 Leaf Area Index
Leaf area index (LAI) was taken at tasseling. Five plants were randomly selected from
each plot, and measurements of the length and the widest part of each leaf of each plant
taken. Each leaf area ‘A’ was estimated by the relationship A = L x B x 0.75, where ‘L’ is
leaf length and ‘B’ is the maximum leaf width (cm). The summation of all leaf area (total
leaf area) was divided by the summation of the ground area occupied by all the selected
plants (5). Thus, LAI = Total Leaf Area / Total Land Area (Saxena and Singh, 1965).
54
3.4.4.4 Maize Dry Matter Yield
Dry matter yield of maize was determined at 6WAP and at harvest in both years. Three
plants were sampled at random from plant rows next to the border rows (i.e. the 2nd and
5th rows) per plot, and cut at ground level. The plants were oven-dried for 48h at 75oC
and weighed. The mean weight of the three plants was calculated to determine the dry
matter yield per plant.
3.4.4.5 Days to 50% Silking
Days to 50% silking was determined by noting the days after planting that 50% of the
plants in the middle four rows had produced silk.
3.4.5 Maize Yield and Yield Components
3.4.5.1 Maize Grain Yield
Harvesting of maize was carried out on the 12th December, 2009 and 15th July, 2010 for
the first and second experiments,respectively; when plants had been considered matured
and dried at 90DAP. The two middle rows per plot were used to assess final grain yield.
Cobs of all plants from each harvestable area were harvested, dehusked and weighed.
Plot by plot grain moisture content at harvest was determined with a protimeter at the
Department of Agricultural Mechanization of the University of Education, Winneba,
Mampong-Ashanti. The cob weight and grain moisture yields were used to determine the
grain yield per plot.
55
3.4.5.2 100-Seed Weight
All harvested ears of plants from the harvestable area were dehusked and shelled. Three
set of one hundred grains were randomly selected per plot and oven-dried in brown
envelopes at 75oC for 48h. The three sets of grain were weighed and the average
determined for 100-seed weight per plot.
3.4.5.3 Harvest Index
Five plants were randomly selected from the 2nd and 5th rows per plot for determination
of harvest index (HI). The plants were cut at ground level, their shoots were oven-dried at
75oC for 48h and were weighed. Cobs on the weighed shoots were dehusked and shelled,
and the grains were weighed. The proportion of the weight of grains to weight of shoot
was computed to determine the harvest index per plot and, subsequently, per treatment.
3.4.6 Economic Returns or Partial Budget Analysis
The prices for both inputs and outputs were collected in both 2009 and 2010 from the
farmers and local markets. Labour data were recorded from farmers using the ‘by-day’
charges at Mampong-Ashanti (Appendix 4).
Partial budget analysis was used to estimate the net benefit (NB) of the treatments and the
marginal rates of return (MRR) to determine the benefit to farmers (CIMMYT, 1998).
The net benefit and MRR were calculated as:
Net benefit (NB) = Total Gross Benefit (TGB)-Total Variable Cost (TVC)
MRR= (∆NB / ∆TVC) x 100
56
The MRR is the increased benefit of a treatment as a percentage of the increased cost.
Dominance analysis was also carried out. A treatment with a lower NB but a higher TVC
compared to another treatment is said to be dominated. No capital costs such as land and
management charges, interest on operational capital, depreciation of machinery and
equipment, and other overheads were considered.
The value of the crop was at harvesting period; therefore, no cost was borne for storage.
Average net returns were calculated as the mean of the seasonal net returns over the study
period.
3.5 Data Analysis
The data collected on weeds and maize crop were subjected to statistical analysis using
Analysis of Variance and the SAS Statistical Package (SAS, 1999).
Significant Difference (LSD) test was used to compare all treatments means.
57
The Least
CHAPTER FOUR
RESULTS
4.1 Climatic Conditions at the Site
Tables 4.1 and 4.2 show the rainfall, relative humidity and temperature at the site during
the 2009 and 2010 cropping seasons. The total monthly rainfall during the 2009 cropping
season ranged from 33.4mm to 138.6mm and the total rainfall received during the
cropping the season was 316.5mm. In 2010, the total monthly rainfall ranged from
77.3mm to 225.8mm, while the total rainfall received during the crooping season was
also 494.9mm.
During the 2009 cropping season, there was a sharp drop in total monthly rainfall from
138.6mm in October to 45.2mm in November after an initial increase in rainfall from
99.3mm in September to 138.6mm in October. In 2010, however, the monthly rainfall
increased from 77.3mm in April to 108.8mm in May and increased further to 225.8mm in
June before reducing to 83.0mm in July.
The mean monthly temperature figures at this location ranged from 22.1oC to 32.7 oC in
2009 and from 21.7oC to 33.8oC in the 2010 cropping seasons.
The mean monthly relative humidity of the area ranged from 56% in both seasons to 98%
in 2009 and 97% in 2010 cropping seasons.
58
Table 4.1: Climatic conditions during 2009 cropping season
Month
Total
Monthly
Rainfall
(mm)
Mean Monthly Relative
Humidity %
(Hours GMT)
Mean Monthly Max.
and Min. Temperature
(oC)
6.00
15.00
Min.
Max
September
99.3
97
71
22.1
29.5
October
138.6
98
67
22.1
30.9
November
45.2
98
60
22.2
32.0
December
33.4
97
56
23.1
32.7
Total
316.5
-
-
-
-
Mean
79.1
97.5
63.5
22.3
31.5
(Meteorological Service Department, Mampong, 2009)
Table 4.2: Climatic conditions during 2010 cropping season
Month
Total
Monthly
Rainfall
(mm)
Mean Monthly Relative
Humidity %
(Hours GMT)
Mean Monthly Max.
and Min. Temperature
(oC)
6.00
15.00
Min.
Max
April
77.3
94
56
23.4
33.8
May
108.8
96
63
23.3
32.4
June
225.8
97
68
22.3
30.9
July
83
97
69
21.7
29.6
Total
494.9
-
-
-
-
Mean
123.7
96
64
22.7
31.7
(Meteorological Service Department, Mampong, 2010)
59
4.2 Soil Characteristics
The physico-chemical properties of soil (0-20cm depth) at the experimental sites are
presented in Table 4.3. Results of soil analysis show that the textural class of the soil in
both years was sandy-loam.
In both years, soil pH was moderately acidic and the level of exchangeable calcium,
magnesium, potassium and sodium were low. Percentage soil organic matter was
moderate (1.79%) in 2009 and low (1.26%) in 2010. Similarly, total N was low and
moderate in 2009 and 2010, respectively.
Table 4.3: Physico-chemical properties of soil at the experimental site in 2009 and 2010
Property
2009
2010
pH (1:2.5 water)
5.8
5.8
Total Nitrogen (%)
0.09
0.15
Organic Matter (%)
1.79
1.26
Exchangeable Calcium (Cmol+/Kg)
5.07
6.4
Exchangeable Magnesium (Cmol+/Kg)
2.4
2.5
Exchangeable Potassium (Cmol+/Kg)
0.47
0.46
Exchangeable Sodium (Cmol+/Kg)
0.15
0.2
Sandy-Loam
Sandy-Loam
Texture
4.3 Weeds Assessments
Table 4.4 shows weed score, percentage weed control and weed control efficiency as
affected by Lumax rates in 2009 and 2010.
60
4.3.1 Weed Score
From visual observation within the marked quadrat areas, at two weeks after planting,
mean weed score was relatively higher for 2010 than 2009. Both Unweeded and Hoeweeded treatments recorded the maximum weed scores of 3.75 in 2009 and 4.00 in 2010
respectively.
Table 4.4: Weed score, percentage weed control and weed control efficiency as affected
by Lumax rates in 2009 and 2010
Weed Score
Percentage Weed
2WAP
Control 6WAP
Treatment
Weed Control
Efficiency (%) at
Harvest
2009
2010
2009
2010
2009
2010
Unweeded
3.75
4.00
0.00
0.00
0.00
0.00
2l Lumax/ha
2.25
2.75
55.40
49.29
69.07
58.81
4l Lumax/ha
0.25
0.00
84.32
76.69
88.29
75.83
6l Lumax/ha
0.25
0.00
89.48
76.93
95.21
77.85
8l Lumax/ha
0.00
0.00
89.18
77.53
95.59
76.06
Hoe-weeded
3.75
4.00
82.52
87.70
97.21
91.18
Mean
1.71
1.79
66.82
61.36
74.23
63.29
LSD (0.05)
0.71
0.31
16.07
5.89
8.34
7.76
CV (%)
27.42
11.39
15.96
6.37
7.45
8.14
Weed score: 0 = not weedy, 1 = moderately weedy, 2 = weedy, 3 = very weedy,
4 = highly weedy
The differences in weed scores among Lumax rates of 4, 6 and 8l/ha were not significant
in both years. However, weed scores for 2l Lumax/ha were significantly (P<0.05) higher
than the weed scores for 4l Lumax/ha, 6l Lumax/ha and 8l Lumax/ha, but significantly
61
lower than the weed scores for Unweeded and Hoe-weeded treatments in both cropping
seasons.
4.3.2 Percentage Weed Control
At 6 weeks after planting, mean percentage weed control was higher in 2009 than in 2010
by 5.46%. In 2009, 4l Lumax/ha, 6l Lumax/ha and 8l Lumax/ha treatments recorded
similarly high percentage (84-89%) weed control that was not significantly different from
the percentage weed control for Hoe-weeded check, but was significantly higher than the
percentage weed control for 2l Lumax/ha treatment. However, in 2010, Hoe-weeded
treatment recorded the highest percentage weed control (88%) that was significantly
(P<0.05) higher than those of 4l Lumax/ha, 6l Lumax/ha and 8l Lumax/ha which effects
were statistically similar, but significantly (P<0.05) higher than that of 2l Lumax/ha.
4.3.3 Weed Control Efficiency
Table 4.4 shows that all the Lumax treatments and Hoe-weeded treatment in general had
more than 58% weed control efficiency. The mean weed control efficiency of the various
rates of Lumax and Hoe-weeded treatments at maize harvest was higher in 2009 (74%)
than in 2010 (63%). In 2009, the maximum weed control efficiency of 97% was observed
under Hoe-weeded treatment, followed by 8l Lumax/ha (96%), 6l Lumax/ha (95%) and
4l Lumax/ha (88%). However, in 2010, Hoe-weeded treatment recorded the highest weed
control efficiency of 91.18%, which was significantly (P<0.05) higher than that in
4lLumax/ha, 6l Lumax/ha and 8l Lumax/ha which were also statistically similar, but
significantly (P<0.05) higher than that in 2l Lumax/ha.
62
4.3.4 Weed Density
Figures 4.1 and 4.2 illustrate weed density as affected by Lumax rates and Hoe-weeded
treatments during the 2009 and 2010 cropping seasons respectively. It was observed that
weed densities recorded under all Lumax treatments and Hoe-weeded treatment were
significantly (P<0.05) lower than those under the Unweeded treatment from 4 to 12 WAP
in both years.
63
Weed densities ranged from 47.5 to 677.8 plants/m2 in 2009 and from 17 to 638 plants/m2
in 2010. Generally, weed densities reduced from 4WAP to 12WAP in all treatments in
both years.
Mean weed densities were higher in 2009 than 2010 at two-week intervals from 4WAP to
12WAP. Treatment effect on weed densities under Lumax rates 4l/ha, 6l/ha and 8l/ha
were similar in both years. After the second hoe-weeding at 6WAP, Hoe-weeded
treatment gave the least weed density which was significantly (P<0.05) lower than weed
densities under all other treatments at 8WAP in 2010.
4.3.5 Weed Flora
Data on composition of weed flora as affected by Lumax and Hoe-weeded treatments at
6WAP in 2009 and 2010 are provided in Table 4.5. The results indicated that the mean
number of sedges was higher than those of grass and broadleaf weeds during both
cropping seasons. The number of grasses, broad leaves and sedges was highest in the
Unweeded treatment in both years. In 2009, compositions of sedges in 4l, 6l and 8l
Lumax/ha and Hoe-weeded treatments were statistically similar, but were significantly
(P<0.05) lower than that of 2l Lumax/ha treatment which also had significantly lower
number of sedges per m2 than in Unweeded treatment. Similarly, in 2010, the number of
sedges found in the 2l Lumax/ha treatment was significantly higher than that of all other
Lumax and Hoe-weeded treatments, but lower than that of Unweeded treatment.
Compositions of grasses and broadleaf weeds found in the 2l Lumax/ha treatment in both
years was significantly lower than the number of grasses and broadleaf weeds per m 2 in
64
the Unweeded treatment (Table 4.5). However, the differences in the compositions of
grasses and broadleaf weeds among the 4l Lumax/ha, 6l Lumax/ha and 8l Lumax/ha and
Hoe-weeded treatments were not significant in both years.
Table 4.5: Weed Flora as affected by Lumax Rates at 6WAP in 2009 and 2010
Grasses
Broadleaf Weeds
2
2
(Plants/m )
Treatment
(Plants/m )
Sedges
(Plants/m2)
2009
91
2010
43
2009
209
2010
192
2009
353
2010
193
2l Lumax/ha
34
11
75
87
202
119
4l Lumax/ha
5
1
7
20
89
75
6l Lumax/ha
5
1
6
22
69
75
8l Lumax/ha
2
1
5
16
59
61
Hoe-weeded
15
1
27
13
79
37
Mean
25
10
55
58
142
93
LSD (0.05)
22
6
49
27
108
29
CV (%)
57
44
59
30
51
21
Unweeded
Results on percentage composition of life form category and dominant species of weeds
in maize as affected by various rates of Lumax treatments and Hoe-weeded treatment
(Appendices 2 and 3) indicated that at 6WAP, the highest weed species diversity was
identified in the Unweeded treatment with the vegetative cover made of grasses
(13.96%), broadleaf weeds (32.02%) and sedges (54.01%) in 2009 and the composition
of 10% grasses, 45% broadleaf weeds and 45% sedges in 2010. The dominant grass
species in the Unweeded control treatment in both years were mainly Echinochloa crusgalli, Rottboela conchichinensis, Sorghum halepens and Panicum maximum (Appendices
2 and 3). For broadleaf weeds the dominant species were Acanthospermum hispidium,
65
Ageratum conyzoides, Bidens pilosa, Euphorbia heterophylla, Commelina benghalensis
and Amaranthus spinosus on the Unweeded control treatment in 2009 (Appendix 2).
Instead of Ageratum conyzoidesbeing among the six dominant broadleaf weed species
that were found in the Unweeded control treatment in 2009 (Appendix 2), Boerhavia
diffusa became the dominant with 35% broadleaf weed species composition (Appendix
3). Boerhavia diffusa also predominated among broadleaf weed species in all other
treatments in 2010 (Appendix 3).
Among Lumax treatments, 2l Lumax/ha treatment was the highest in weed species
diversity in both years. Cyperus rotundus was the sole sedge species that predominated
across all treatments on the experimental fields in both cropping seasons (Appendices 2
and 3).
4.3.6 Weed Dry Matter
Table 4.6 shows weed dry matter as affected by Lumax rates in 2009 and 2010.
Table 4.6: Weed dry matter as affected by Lumax rates in 2009 and 2010
Treatment
Unweeded
2l Lumax/ha
4l Lumax/ha
6l Lumax/ha
8l Lumax/ha
Hoe-weeded
Mean
LSD (0.05)
CV (%)
Weed Dry Matter (g/2)
6WAP
12WAP
2009
2010
2009
2010
162.18
164.06
185.31
208.32
72.95
77.34
60.58
105.62
22.25
38.45
21.73
59.67
12.05
37.96
9
58.34
11.4
37.5
8
58.02
18.4
18.75
5.5
17.71
49.87
62.34
48.35
84.61
39.93
7.11
27.88
26.21
53.12
7.6
38.26
25.55
66
The influence of treatments on weed dry matter accumulation at both 6 and 12 WAP in
both years revealed that 2l Lumax/ha had significantly (P<0.05) lower dry matter weight
than Unweeded treatment, but significantly (P<0.05) higher dry matter weight than did
Lumax rates at 4l/ha, 6l/ha, 8l/ha and Hoe-weeded treatments. At 12WAP in 2009, the
least dry matter of 5.5g/m2 was obtained from Hoe-weeded treatment.
The results indicated that 2l Lumax/ha recorded significantly (P<0.05) higher weed dry
matter values than the other Lumax treatments and Hoe-weeded treatment at both 6WAP
and 12WAP.
Unweeded treatment had significantly higher weed dry matter weights than all Lumax
and Hoe-weeded treatments. Mean weed dry matter weight was higher at both 6WAP and
12 WAP in 2010 than in 2009.
4.4 Vegetative Growth of Maize
Table 4.7 shows the results of the effect of Lumax rates and Hoe-weeded treatments on
percentage crop establishment at 2WAP, leaf area index at tasseling and days to 50%
silking in both years.
4.4.1 Percentage Crop Establishment
Crop establishment ranged from 96.9 to 100% for both years and did not differ
significantly among the treatments.
67
Table 4.7: Maize crop establishment, leaf area index and days to 50% silking as affected
by Lumax rates in 2009 and 2010
Days to 50%
Silking
Crop Establishment
(%) at 2WAP
2009
2010
Leaf Area Index at
Tasseling
2009
2010
2009
2010
Unweeded
98.40
99.55
1.10
1.34
48.50
51.75
2l Lumax/ha
97.80
100.00
1.64
1.41
48.80
51.25
4l Lumax/ha
96.90
100.00
1.98
2.06
48.30
51.25
6l/ha Lumax
97.80
99.10
2.18
2.09
48.80
50.75
8l/ha Lumax
97.10
99.55
2.18
2.00
48.50
51.00
Hoe-weeded
97.30
99.55
2.07
2.02
48.50
50.50
Mean
97.53
99.63
1.86
1.82
48.50
51.08
LSD (0.05)
NS
NS
0.50
0.28
NS
0.97
CV(%)
2.13
0.83
17.97
10.13
1.94
1.26
Treatment
4.4.2 Leaf Area Index at Tasseling
Mean leaf area index was slightly higher in 2009 than 2010. In both seasons, Unweeded
treatment gave the least leaf area index. In 2009, maximum leaf area index was produced
by 6l Lumax/ha and 8l Lumax/ha, which was not significantly different from those on 4l
Lumax/ha and Hoe-weeded treatments, but was significantly higher than those of 2l
Lumax/ha and Unweeded treatments. In 2010, the influence of weed control treatments
on leaf area index showed that Hoe-weeded treatment and Lumax rates at 4l/ha, 6l/ha,
8l/ha had similar leaf area index which was significantly (P<0.05) higher than the leaf
area index for 2l Lumax/ha and Unweeded treatments, both of which had similar effects.
4.4.3 Days to 50% Silking
Days to 50% silking ranged from 48.3-48.8 in 2009 and from 50.5-51.75 in 2010. The
maize plants delayed silking in 2010 compared with 2009. In 2010, Hoe-weeded and 6l
68
Lumax/ha treatments had significantly lesser days to 50% silking than Unweeded
treatment.
4.4.4 Plant Height
Figures 4.3 and 4.4 show treatment effects on maize plant height in 2009 and 2010
respectively.
Maize plant height did not differ significantly among all treatments over the periods of
sampling.
69
4.4.5 Maize Shoot Dry Matter
Data on maize shoot dry matter as affected by various rates of Lumax treatments and
Hoe- weeded treatment at 6WAP and at harvest in both years are presented in Table 4.8.
Generally, maize plants accumulated more shoot dry matter at both 6WAP and at harvest
in 2010 than in 2009.
During both periods in 2009, Unweeded treatment recorded the least dry shoot biomass
that was significantly (P<0.05) lower than that obtained with other treatments. However,
in 2010, Unweeded treatment gave dry matter weights similar to that of 2l Lumax/ha, but
significantly (P<0.05) lower than the shoot dry matter obtained with other treatments.
Table 4.8: Maize shoot dry matter as affected by Lumax rates in 2009 and 2010
Maize Shoot Dry Matter (g/plant)
6WAP
Treatment
13WAP (Harvest)
2009
2010
2009
Unweeded
255.69
274.59
425.88
468.75
2l Lumax/ha
325.46
295.93
478.08
620.31
4l Lumax/ha
393.47
394.38
699.89
867.94
6l Lumax/ha
376.87
391.07
699.70
863.94
8l Lumax/ha
389.16
393.45
666.59
868.39
Hoe-weeded
365.26
412.75
639.59
871.96
Mean
350.99
360.36
601.62
760.22
52.04
30.88
20.67
9.8
5.7
2.3
LSD (0.05)
CV (%)
70
2010
169
14.8
4.5 Yield and Yield Components of Maize
4.5.1 100-Seed weight
The results in Table 4.9 indicate that during the 2009 cropping season, 100-seed weight
ranged from 28.75g for Unweeded treatment to 30.5g for 4l Lumax/ha treatment. In
2010, the Unweeded treatment recorded the least 100-seed weight of 36.0g as compared
to 37.25g and 41.25g recorded by 2l Lumax/ha and 8l Lumax/ha treatments, respectively.
Generally, 100-seed weight for all treatments was higher in 2010 than 2009.
Table 4.9: 100-seed weight, grain yield and harvest index as influenced by Lumax and
hoe-weeding, 2009 and 2010
Treatment
100-Seed
Weight (g)
Grain Yield
(t/ha)
Harvest Index
2009
2010
2009
2010
2009
2010
Unweeded
28.75
36.00
3.07
4.44
0.37
0.28
2l Lumax/ha
29.25
37.25
4.01
5.20
0.38
0.29
4l Lumax/ha
30.50
40.50
5.07
6.50
0.42
0.33
6l Lumax /ha
30.25
40.75
5.10
6.52
0.41
0.34
8l Lumax/ha
30.25
41.25
5.08
6.55
0.41
0.34
Hoe-weeded
30.00
41.00
5.00
6.50
0.41
0.33
Mean
29.83
39.46
4.56
5.95
0.40
0.32
LSD (0.05)
0.06
0.04
0.02
0.86
NS
0.04
8.43
0.30
9.53
9.91
8.43
CV (%)
9.91
71
4.5.2 Grain Yield
Grain yields ranged from 3.07-5.10 t/ha and 4.44-6.52 t/ha in 2009 and 2010, with mean
grain yield of 4.56 t/ha and 5.95 t/ha, respectively (Table 4.10).
In both 2009 and 2010, Unweeded treatment recorded the least grain yield values. In
2009, grain yield under Unweeded treatment was significantly (P<0.05) lower than that
under 2l Lumax/ha treatment, but in 2010, differences in grain yield between between
these two treatments were not significant. Similarly, although in 2009, Hoe-weeded
treatment gave a grain yield that was significantly lower than those of 4l, 6l and 8l
Lumax/ha treatments, in 2010, Hoe-weeded treatment produced a grain yield that was
similar to same treatments. The 2l Lumax/ha treatment supported the least grain yield
among Lumax treatments.
4.5.3 Harvest Index
Values for harvest index ranged from 0.37 to 0.42 in 2009 and from 0.28 to 0.34 in 2010
with the mean harvest index of 0.40 in 2009 and 0.32 in 2010. In 2009, there were no
significant (P>0.05) differences in harvest index among treatments. However, in 2010,
the Unweeded treatment gave the least harvest index, which was significantly lower than
the harvest indexes for 4l, 6l and 8l Lumax/ha treatments and Hoe-weeded treatment.
There were, however no significant differences in harvest indexes among Lumax
treatments at rates 4l, 6l, 8l Lumax/ha and Hoe-weeded treatment.
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4.6 Correlation between maize grain yield and yield component, weed and weed
control variables in 2009 and 2010
Data in Table 4.10 reveals that during both years of the study, weed density at 12WAP
recorded highly significant negative correlation with grain yield at r = -0.76 and r = -0.80
respectively.
Similarly, weed dry matter at 12WAP gave highly significant negative correlation with
grain yield at r = -0.93 and r = -0.76 in 2009 and 2010 respectively (P≤0.01).
On the other hand, percentage weed control at 6WAP as well as 100 maize seed weight,
and weed control efficiency at harvest highly positively correlated with maize grain yield
in both years.
Table 4.10: Correlation between maize grain yield and yield component, weed and
weed control variables
Correlation with Grain
Yield
Variable
2009
2010
Percentage Weed Control at 6WAP
0.95**
0.84**
Weed Density at 12WAP
-0.76**
-0.80**
Weed Dry Matter at 12WAP
-0.93**
-0.76**
Weed Control Efficiency at Harvest
0.96**
0.80**
100 Seed Weight
0.90**
0.90**
** = Highly significant (P<0.01)
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4.7 Economic Analysis
The economic analysis was based on costs provided in Appendix 4. Data on partial
budget analysis for maize as affected by Lumax rates and two hoe-weedings during the
two cropping seasons are presented in Tables 4.11 and 4.12. The grain yields were
adjusted by 10% in the analysis.
The analysis showed that in general, all treatments had positive net benefits. However,
the 4l Lumax/ha had the highest net benefit among the treatments. The Unweeded
(Control) as expected gave the least net benefit in both years. The dominance analysis
showed that the 6l Lumax/ha, Hoe-weeded and 8l Lumax/ha treatments had lower net
benefits but higher total variable costs than the 4l Lumax/ha treatment, and therefore,
were dominated in both 2009 and 2010.
The 8l Lumax/ha gave higher net benefits than the Hoe-weeded treatment in both years.
However, applying Hoe-weeded treatment over 8l Lumax/ha gave a marginal rate of
return (MRR) of 69% in 2009 and 24% in 2010. Applying the 2l Lumax/ha over the
Unweeded (control) gave a MRR of 371% in 2009 and 294% in 2010 while applying 4l
Lumax/ha over the 2l Lumax/ha gave a MRR of 501% and 714% in 2009 and 2010
respectively.
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75
76
CHAPTER FIVE
DISCUSSIONS
5.1 Climatic Conditions at the Site
Total rainfall during the 2010 season was higher than in 2009 hence maize growth and
yield production was better in the former period. It must be noted that the 2009 planting
was done in the minor season, and the 2010 planting was done the major season. Supply
of water is particularly important from the tasseling to grain filling stage of maize growth
if severe reduction in yield is to be avoided. The results of the current study showed a
sharp drop in total monthly rainfall from 138.6mm in October to 45.2mm in November,
2009 when maize plants had reached the tasseling-to-silking stage and might
consequently reduce grain yield. Awuku et al. (1991) and Tweneboah (2000) indicated
the tasseling-to-silking stage of maize growth as a critical period that requires enough
moisture for high yields. Adjetey (1994) reiterated that to obtain high yield, it is
important that water deficits do not occur prior to tasseling till the completion of grain
filling. He noted that of all the growth stages maize, this is the most sensitive period to
water shortage.
The mean monthly temperature figures that ranged from 22.1 to 32.7 oC in 2009, and
from 21.7 to 33.8 in the 2010 cropping seasons were adequate for maize growth and yield
during both seasons. According to Awuku et al. (1991), maize requires an average
temperature range of 13-40 oC and does not grow well to give high yields at higher
temperatures.
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5.2 Physico-chemical properties of soil
Akobundu (1987) reported that soil texture and organic matter were the most important
factors which influenced herbicide activity in the soil. The soil texture at the experimental
site during both years was sandy-loam, while percentage organic matter was moderate in
2009 and low in 2010. These characteristics of the soil indicated that the applied
herbicide could be made available for optimum uptake because the relatively low clay
and organic matter content of the soil will not absorb much of the applied herbicide to
render it unavailable for weed uptake and herbicidal activity. This assertion corroborates
Ayeni and Yakubu (1995), who reported that high clay and organic matter levels of the
soil absorb some fraction of the applied herbicide and rendered it unavailable for plant
uptake and herbicidal activity. On the other hand, low carbon in the soil of a maize field
in Ibadan made applied herbicide available for optimum uptake (Makinde and
Ogunbodede, 2007).
The medium and low percentage organic matter of 1.7 and 1.26 in 2009 and 2010,
respectively as well as the sandy-loam textural class of the soil were adequate for
effective weed control in maize using the range of Lumax application rates of 2-8l/ha.
According to Syngenta (2009), in most cases, Lumax should be applied at 7l/ha; but in
soils with less than 3% organic matter, Lumax may be applied at 5.9l/ha.Wenzel (2002)
reported that on heavier soils at Arlington, the recommended rate of 7l/ha provided the
best results, and lower rates had correspondingly more escapes. Lighter soils had
equitable results with a lower 5.9l/ha rate, which the Sygenta Company recommends for
soils with organic matter less than 3% (Wenzel, 2002). Although large-scale maize
production takes place on soils with a clay content of less than 10% (sandy soils) or in
78
excess of 30% (clay and clay-loam soils), the texture class between 10 and 30% have air
and moisture regimes that are optimal for healthy maize production (DARSA, 2003).
Baffour (1990) shared similar opinion indicating that clayey sandy soils were not as
conducive as loams and loamy-soils for maize growth.
Two soil factors that may affect the rate of atrazine degradations are soil pH and organic
matter. The moderately acidic condition of the soil (Table 4.2) would increase the rate of
degradation of atrazine (one of the constituents of Lumax) because atrazine is a weak
base and absorbs less as soil pH increases (Goetz et al., 1989). Soil pH has a greater
effect on the rate of degradation than organic matter or other soil properties (Ferris et al.,
1989) with a decrease in the rate of degradation as pH increases (Ferris et al., 1989;
Houot et al., 2000).The soil pH of 5.8 and textural class of sandy loam in both cropping
seasons indicated their suitability for effective herbicide activity and healthy maize
production. While Tweneboah (2000) and Safo (1994) were of the view that the pH range
of 5.5-5.7 was the optimum for maize production, Adjetey (1994) stated that the pH
should not be less than 4.5.
5.3 Weeds Assessment
5.3.1 Weed Score
Aflakpui et al., (2005) stated that weeds have a competitive ability over young maize
seedlings and therefore it is necessary to keep fields free from weeds at least in the 4-6
weeks after sowing. The need to control weeds during the early stages of the crop is
known to be critical (Evans et al., 2003). Application of a good contact or systemic
herbicide prior to planting ensures that maize field is free from weeds during the critical
79
growth stage of the crop and still gives the best yield and economic return (Bradley et al.,
2000; Hamill et al., 2000).
Various rates of Lumax application influenced weed score in both years. The Unweeded
and Hoe-weeded treatments which received no pre-emergence herbicide treatment were
highly weedy with weed scores of 3.75 and 4.0 in 2009 and 2010 respectively. However,
treatments that received pre-emergence application of Lumax at rates ranging from 28l/ha had significantly lower weed score than the Unweeded and Hoe-weeded treatments.
Gana et al. (2008) similarly reported that all herbicide treatments had similar weed cover
scores which were significantly lower than those of the weedy check and hoe-weeded
control at 3WAP. While weeds under Unweeded and Hoe-weeded treatments were left to
germinate after initial land preparation and sowing, weed seedling emergence early in the
season was inhibited by Lumax, an inhibitor of the enzyme p- hydroxy phenylpyruvate
dioxygenase (Hartzler, 2009).
According to Syngenta (2009), Lumax® herbicide controls weeds with three different
modes of action utilizing three components: Atrazine, Mesotrione and S-metolachlor.
Atrazine functions by binding to the plastoquinone-binding protein in photosystem II,
which animals lack. Plant death results from starvation and oxidative damage caused by
breakdown in the electron transport process. Oxidative damage is accelerated at high
light intensity (Appleby et al., 2002). The mode of action of mesotrione has been found
to be by competitive inhibition of HHPD (hydroxy-phenyl-pyruvate dioxygenase)
enzymes which is part of the pathway that converts amino acid tyrosine to plastoquinone
(Cornes, 2009). The Weed Science Society of America (1997) stated that S-metolachlor
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belongs to the herbicide class chloroacetamides which are meristimatic growth inhibitors
that are translocated. Mesotrione, the broadleaf weed control component in Lumax is
readily taken up by roots and shoots of the plant and then rapidly translocated throughout
the plant via both xylem and phloem. Intake of the two remaining ingredients occurs
readily through the roots and/ or shoots of germinating weed seedlings and then moves in
the xylem (Syngenta, 2009).
The treatment, 4l Lumax/ha appeared to be the most promising in weed control. Although
at a lower concentration applied per unit area, 4l Lumax/ha treatment had a lower weed
score that was not significantly different from the weed scores for 6l Lumax/ha and 8l
Lumax/ha treatments. Increase in public concern for the protection of the environment
and increased awareness of pesticide residues in food and water, have necessitated
intensive studies into possibilities to reduce herbicide use in maize production. A major
possibility is the use of lower doses of herbicides (Mulder and Doll, 1993; Rola et al.,
1999). The use of lower herbicide doses is the simplest way for reducing herbicide use
without changing the production technology significantly.
Many reports recognize that doses of herbicide can be lowered by 15 to 30% without a
significant impact on maize yield loss in situations with moderate weed pressure (Rola et
al., 1999; Schans and Weide, 2000). Some authors have also established that greater
reductions of herbicide doses (50-70%) can provide satisfactory weed control and good
economic return in suitable conditions (Forcella, 1995; Schans and Weide 2000). A few
experiments revealed possibilities of 80% (Alm et al., 2000), or even 90% (Weide et al.,
1995) of herbicide dose reduction without risk of significant increase in yield losses.
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The weed score for 2l Lumax/ha was significantly higher than those for 4l Lumax/ha, 6l
Lumax/ha, 8l Lumax/ha and Hoe-weeded treatments. The 2l Lumax/ha was considered as
a sub-lethal dose. By using sub-lethal doses, weeds are not controlled totally (incomplete
weed kill). After a relatively short period, the weeds can regrow if they are not
additionally suppressed by maize (Lešnik, 2003). Lešnik (2003) also noted that in the
case of broadcast application, the reduction of herbicide doses by 10-25% could be
advised to farmers, if weed population consists of less than 100 plants per m2. Mulder
and Doll (1993), Rola et al., (1999) and Zhang et al. (2000) also reported that 15-30%
reductions of herbicide doses could be advised to maize producers when they have to
control moderate weed populations and maize has good competitive ability.
5.3.2 Percentage Weed Control and Weed Control Efficiency
Lumax treatments at all rates reduced weed density significantly compared to Unweeded
treatment in both years. Similar observations were reported by Patel et al. (2006), Gana et
al. (2008) and Chikoye et al. (2006). The better weed control under Lumax treatments
than Unweededtreatment might be due to longer persistence of Lumax up to 6WAP.
Syngenta (2009) indicated that Lumax delivers long-lasting residual control for six weeks
or more, which makes it a perfect fit for use in both conventional and glyphosate-tolerant
corn.
In both years, 4l Lumax/ha treatment had a percentage weed control that was similar to
those of 6l Lumax/ha and 8l Lumax/ha. In contrast, 2l Lumax/ha had significantly lower
percentage weed control than the higher doses of Lumax perhaps because of the sub82
lethal dosage of the 2l Lumax/ha for weed control. The trend of weed control among
various rates of Lumax at 6WAP was similar to the trend in weed score at 2WAP in
which differences in weed scores among Lumax treatments at 4l/ha, 6l/ha and 8l/ha were
similar, but differed significantly from that of 2l Lumax/ha treatment.
Weeds were left uncontrolled under Hoe-weeded treatment until 3WAP. Maize grown in
the presence of weeds would have less developed root system for absorption of nutrients
and water than when grown without weeds. Also, weed root exudates contain toxins that
could inhibit root growth in maize (Rajcan and Swaton, 2001).
Although plots of Hoe-weeded treatment were significantly more weedy than Lumaxtreated plots at 2 WAP, after the first hoe-weeding at 3 WAP, percentage weed control at
6WAP under the Hoe-weeded treatment was as effective as those of Lumax treatments at
4l/ha, 6l/ha and 8l/ha in 2009 and even better in 2010. These findings agree with those of
Chikoye et al. (2006) who reported that a new formulation of Atrazine at doses of 3.0 to
3.5 kg a.i/ha gave effective weed control comparable to the hoe-weeded treatment.
However, Prematilake et al. (2004) reported that weed control with herbicide was
superior to that of hand weeding. They explained that manual weed control was less
efficient and its cost was ever increasing. Removing weeds manually is very labourintensive and therefore expensive (Riches et al., 2005; Kibata, 2002; Chikoye et al.,
2002; Yadav, 2003). Yadav (2003) for example, reported that traditional methods of hand
weeding, in addition to being expensive and time consuming were ineffective in
controlling weeds as new weed seeds germinated after every hoeing and re-infested the
field competing with the crop. Moreover, hoeing is not possible during raining season
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and labour shortage at that time further accentuates the problem (Parker and Vernon,
1982).
5.3.3 Weed Control Efficiency
Weed control efficiency (WCE) for all Lumax treatments and Hoe-weeded treatment in
general has more than 58%. In 2009, the maximum weed control efficiency of 97.21%
was observed under Hoe-weeded treatment followed by 8l Lumax/ha (95.59%), 6l
Lumax/ha (95.21%) and 4l Lumax/ha (88.29%). Higher weed control efficiency recorded
under these treatments was as a result of better control of all weed types by Lumax
herbicide and manual removal of weeds by Hoe-weeded treatment (Patel et al., 2006).
In 2010, Hoe-weeded check recorded the highest weed control efficiency of 91.98%
which was significantly (P<0.05) higher than Lumax treatments of all rates of
application. Shah and Koul (1990) and Thakur (1994) observed higher WCE under twice
hand weeding carried out at 20 and 40 days after sowing in maize crop.
5.3.4 Weed Density
All Lumax treatments and Hoe-weeded treatment recorded significantly lower weed
densities than did Unweeded treatment in both seasons, as reported by Vaseloskii (1993),
Khan and Haq (2004) and Subhan et al. (2007). Generally, there was a reduction in weed
density from 4WAP to 12WAP under all treatments in both years. Higher weed density at
4WAP might mean that there was a high weed seed population in the soil with high
germination capacity that responded positively to favourable environmental factors and
many weed seedlings were able to survive at 4WAP. According to Hamayun (2003), at
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this stage in the growth of the seedling weeds and crops, much negative interaction might
have not set in. However, as weed and crop seedlings grew older and developed more
structures such as roots and root hairs as well as photosynthetic apparatus necessary for
tapping the growth factors in the plants’ environment, competition among seedlings for
the growth factors as well as allelopathy was intensified. Weeds that were more
aggressive, persistent and resistant to control might have outgrown, smothered and killed
the weaker ones, and thereby progressively reduced weed population during the growth
period up to 12WAP (Hamayun, 2003).
The importance of weed competition in maize depends on four factors: the crop growth
stage, the amount of weeds present, the degree of water and nutrient stress, and the weed
species. Weeds damage the crop primarily by competing for light, water and nutrients
(Tollenaar et al., 1997b).
The 4l Lumax/ha treatment gave weed densities that were not significantly different from
weed densities under 6l Lumax/ha and 8l Lumax/ha treatments from 4 to 12WAP during
both cropping seasons. This trend in weed density was similar to the trend in weed
scores, where no significant differences were found among 4l Lumax/ha, 6l Lumax/ha
and 8l Lumax/ha treatments at 2WAP. These trends in both weed density and weed score
might be attributable to the similar effective weed control among the three treatments.
The trend in weed density under Hoe-weeded treatment was as a result of the effect of the
second hoe-weeding at 6WAP that reduced weed population at 8WAP followed by regrowth of weeds before 10WAP and 12WAP. Although, hoe-weeding reduced weed
85
density comparable with 4l, 6l and 8l Lumax/ha treatments, Chikoye et al. (2004)
reported that weeds and shortage of labour for their removal were two of the most
important production constraints in smallholder farms. Smallholder farmers spent 5070% of their total available farm labour on weed control by hoe-weeding in maize.
5.3.5 Weed Flora
The most predominant weed flora across the experimental field during both cropping
seasons was sedges. Grass weeds were the least common. Lumax treatment at 2l/ha left
significantly higher compositions of grasses, broadleaf weeds and sedges than did other
Lumax treatments during the 2009 cropping season, indicating that 2l Lumax/ha could
not control the three categories of weeds as effectively as the others.
Although Panicum maximum and Acanthospermum hispidium (grass weeds) as well as
Amaranthus spinosus (broadleaf weed) appeared as dominant weed species under
Unweeded control treatment, they were almost absent under all Lumax treatments in both
cropping seasons. This showed that these types of grass and broadleaf weed species were
satisfactorily controlled using 2-8l/ha of Lumax according to the recommendations by
Syngenta (2009) that pre-application of Lumax provides high-performance, broadspectrum control of the toughest grasses and broadleaf weeds.
Cyperus rotundus (purple nut sedge) the predominant sedge species that infested the crop
across all treatments on the experimental fields during both cropping seasons. Darkwa et
al. (2001) noted that Cyperus rotundus dominated a maize field and prevented potential
86
maize yields being reached in Ghana due to high tuber populations of C. rotundus that
favourably competed with maize roots for water, nutrients and space.
There were less numbers of sedges under Lumax treatments than under Unweeded
treatment. This indicates that there was some level of control of sedges by the Lumax
rates. Hager and Sprague (2007) found that Lumax controls annual grasses, annual
broadleaf weeds and sedges in corn. However, higher composition of sedges than grass
and broadleaf weeds under Lumax treatment depicted higher susceptibility of grass and
broadleaf weeds to control by Lumax than sedges.
Although, Chikoye et al. (2009) pointed out that Lumax at all rates (1.88-2.96 kg a. i.)
controlled sedges as effectively as hoe-weed control (95-100%), the findings of this
current study showed that during the 2009 cropping season, sedge composition under
Lumax treatments of rates 4l/ha, 6l/ha and 8l/ha was similar to that of Hoe-weeded
treatments, but significantly lower than that of 2l Lumax/ha treatment. Moreover, in
2010, the composition of sedges under Hoe-weeded was at par with that under 8l/ha
Lumax treatment, but lower than those under rates 6l/ha, 4l/ha and 2l/ha (Table 4.5). This
indicated a better sedge control by Hoe-weeded and 8l/ha Lumax treatment than the
lower rates of Lumax treatments. In contrast, Lum et al. (2005) reported that hand
weeding were very popular, but used up lots of labour and were not effective on
underground rhizomes.
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5.3.6 Weed Dry Matter
Weeds under Unweeded treatment produced significantly more dry matter than did weeds
found under Lumax treatments and Hoe-weeded treatment. These findings corroborate
Chikoye et al. (2005) who also reported that hoe-weeded control and all herbicide
treatments tested gave lesser dry matter than did Unweeded control. Compared to
Unweeded treatment, Lumax treatments at all rates and Hoe-weeded treatment had lower
weed dry matter probably because they provided better weed control and had lower weed
densities. These findings are in agreement with Olunuga and Objimi (1983), who
attributed reduced weed dry matter in maize to the effectiveness of primextra (a preemergence herbicide) in weed control with its corresponding lowered weed density.
Compared to traditional method of hand weeding and hoeing, Yadav (2003) reported that
the usage of pre-emergence herbicide proved best, reducing the dry weight of weeds by
80 to 88%.
Chikoye et al. (2006) reported that there was a rate of decrease in dry matter as the
herbicide dose increased. This does not agree with the results of the present study in
which the increase in Lumax rates from 4l/ha to 6l/ha and from 6l/ha to 8l/ha showed no
significant differences in weed dry matter. At 6WAP and 12WAP in 2009, and from
4WAP to 12WAP in 2010, the 4l Lumax/ha treatment consistently maintained weed dry
matter weight that were at par with those under 6l and 8l Lumax/ha treatments although
4lLumax/ha had lower concentration per unit area. This trend of weed dry matter
production among 4l/ha, 6l/ha and 8l/ha Lumax treatments was the same as trends in
weeds score at 2WAP, percentage weed control at 6WAP, weed density from 4WAP to
12WAP and weed control efficiency at harvest in both years.
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In 2010, weed dry matter weight rose from 12.75g/m2 at 4WAP to 19.51g/m2 at 6WAP
followed by a sharp drop in weed dry matter weight values from 19.51g/m2 at 6WAP to
4.8g/m2 at 8WAP under Hoe-weeded treatment (Figure 4.3). This drop in weed dry
matter might be attributed to the effect of hoeing at 6WAP, and was similar to the drop in
weed density due to hoe-weeding during the same period (Figures 4.1 and 4.2). After the
drop in 8WAP, the dry matter weight increased gradually but was significantly lower
than those of all other treatments through 10WAP to 12WAP. This trend in dry matter
weight increase under Hoe-weeded treatment from 8WAP to 12WAP, however did not
reflect the trend in weed density under Hoe-weeded treatment in which weed densities
remained low and were similar to those of Lumax at 4l/ha, 6l/ha and 8l/ha treatments at
10WAP and 12WAP after a reduced weed density at 8WAP. After a second hoe weeding
at 6WAP until 12WAP, Hoe-weeded treatment had more influence on reducing weed dry
matter than weed density as compared with Lumax treatments at 2 -8l/ha. This may mean
that weeds that emerged in maize after Hoe-weeding at 6WAP up to 12WAP weighed
lesser than weeds that remained during the same period when treated with Lumax at 28l/ha pre-emergence.
In addition to the most promising effect of Hoe-weeding in reducing weed dry matter,
the treatment also provides clean seed bed and loosens the soil. The cut weeds left in the
soil may decompose and add organic matter to the soil for enhanced growth and yield of
maize. However, hoe-weeding predisposes the soil to erosion as a result of the clean
weeding and loosening up the soil. Erosion due to hoe weeding adversely affects crop
productivity by reducing the water- holding capacity of the soil, water availability,
89
nutrient levels and organic matter in the soil, and soil depth (Pimentel et al., 1995).
Conversely, Fawcett and Towery (2002) and Gianessi and Reigner (2006) noted that
herbicides reduce soil disturbance and thereby reduce soil erosion.
Treatments with better weed control efficiency had lower weed dry matter as was shown
at 12WAP in 2010. Hoe-weeded treatment recorded the least dry matter weight and the
maximum weed control efficiency that were significantly different from all other
treatments. Similarly, lower weed dry matter and higher weed control efficiency were
found under Lumax treatments at 4l/ha to 6l/ha and 8l/ha than at 2l/ha.
5.4 Vegetative Growth of Maize
5.4.1 Crop Establishment
The high percentage crop establishment (96.9-98.4%) indicated achievement of optimum
plant population density. High viability and the healthy nature of the maize seeds used as
planting materials contributed significantly to the high percentage crop establishment.
Onwueme and Sinha (1991) and CRI (1996) have emphasized the need to use the most
appropriate planting material (highly viable seeds), optimum planting depth, spacing and
good land preparation to enhance good germination and crop establishment as well as
reduction in weed competition for growth resources later during the season. High mean
monthly rainfall values recorded in the months of August and September, 2009 might
also have contributed to such high percentage crop establishment.
The high percentage crop establishment also portrayed the effectiveness of benoxacor, a
crop safener in Lumax, in ensuring crop safety from herbicide injury. Crop injury can
90
negatively impact germination, establishment, growth and yield. This finding confirms
the assertion that Lumax provides excellent crop safety (Syngenta, 2009). Wenzel (2002)
also noted that the Lumax has an excellent crop safety profile and the corn looked tall and
healthy and was very good for both grain and silage hybrids. The lack of significant
differences in crop establishment in both years suggests that the conditions necessary for
seed germination and crop growth and developments were similar.
Optimum number of plants is an important factor controlling weeds. Nawab et al. (1997)
stated that it would be logical to expect that weed management improves if the optimum
maize population is maintained. The relatively high percentage crop establishment
suggests that such a plant population could have early canopy closure that could suppress
weed growth by preventing sunlight from reaching the weeds beneath them for
photosynthesis. Maize competitive ability depends on maize stand density and the rate of
development. In some environmental and production conditions, usually the high
competitive ability of maize can be reached in stands where density exceeds 8 plants per
m2 (Lešnik, 2003).
For phyto-toxicity of herbicide on crop, each treatment was observed thoroughly but no
such effect was noticed during the study. Ali et al. (2003) made similar observations in
which pre-emergence herbicides caused no injury to maize. Also, in evaluations made at
7 and 18 days after treatments for numbers of injured plants as well as the amount of the
plant expressing the injury, Jemison and Wilson (2002) found no injury to any variety
when mesotrione (Camix or Lumax) was applied pre-emergence. However, Bradley
(2005) reported that corn had been injured as a result of application of mesotrione, one of
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the ingredients of Lumax, Lexar and Camix. He noted that corn had leaves with chlorotic
to a completely bleached-white appearance. Injury usually appeared on the older leaves
while new leaves often appeared normal and unaffected. The author pointed out that
symptoms of the herbicide were usually short-lived and often confined to low areas or
wet spots within a field. In severe cases where a high percentage of the foliage had a
chlorotic or bleached-white appearance, the plants eventually turned brown (necrotic) and
died, and consequently, reduced crop establishment (Bradley, 2005).
5.4.2 Leaf Area Index
At 6 WAP, the trend in the influence of weed control treatments on leaf area index (LAI)
showed that Hoe-weeded treatment and 4l, 6l and 8l Lumax/ha treatments had similar
LAI that was higher than the LAI for Unweeded treatment and 2l Lumax/ha treatments.
Similar trends were noticed in the influence of the treatments on weed density and weed
dry matter during the same period. The probable indication of these findings was that the
LAI for 2l Lumax/ha and Unweeded treatment reduced as a result of high weed
competition for growth factors, especially, for light. The findings of the present study
supported those by Tollenaar et al. (1997b) which revealed that high competitions by
weeds reduced LAI in maize at blooming by 15%. However, Rajcan and Swanton (2001)
observed that most weeds during and after blooming of maize are below 1m, and
therefore direct competition between maize and weeds for incident photon flux was
relatively small (Rajcan and Swanton, 2001).
An implication for the higher LAI under Hoe-weeded and 4l, 6l and 8l Lumax/ha
treatments than 2l Lumax/ha and Unweeded treatments was that, with higher LAI, plants
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under 4l, 6l, 8l Lumax/ha and Hoe-weeded treatments might have intercepted incident
photon flux better, accumulated more dry matter and yielded more grains than plants
under 2l Lumax/ha and Unweeded treatments. According to Rajcan and Swanton (2001),
the LAI defines a plants ability to intercept the incident photons flux and is an important
factor in determining dry matter accumulation. Specifically for maize, Valentinuz and
Tollenaar (2006) noted that leaf area influences the interception and utilization of solar
radiation, and consequently, drive dry matter accumulation and grain yield.
5.4.3 Days to 50% Silking
In 2009, the 4l Lumax/ha treatment recorded the least number of days to 50% silking,
which was not significantly different from days to 50% silking recorded under all other
treatments (P<0.05). Similarly, no significant differences in days to 50% silking among
hoe-weeded, unweeded and herbicide treatments were reported by Subhan et al. (2007).
However, overall, plots treated with weed control methods took more days to silking than
no weeding (Subhan et al., 2007).
In 2010, even with higher weed density and higher weed dry matter weight, Unweeded
control treatment took more days to 50% silking that was significantly higher than those
under Hoe-weeded and Lumax treatments. However, in contrast, Nawab et al. (1997)
pointed out that number of days to silking was increased in weed free plots as compared
to check plots.
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5.4.4 Plant Height
The height of plant is an important growth character directly linked with the productive
potential of plant in terms of fodder, grains and fruit yield. Plant height has been reported
to be positively correlated with productivity of plants (Saeed et al., 2001). Results from
this study showed that Unweeded treatment produced maize with the least height from 28WAP during both cropping years (Figures 4.4 and 4.5). This may be attributed to the
higher weed densities under Unweeded treatment that had competed with maize for
nutrients, soil moisture, light and carbon dioxide, and had considerably reduced maize
height (Hussain, 1983; CRI, 1996). Similarly, Ahmed et al. (1988), Behera and Singh
(1998), Williams et al. (1998) and Riaz et al. (2007) have reported similar results
obtained from various weed control techniques.
Among the herbicide treatments, 4l/ha, 6l/ha and 8l/ha produced taller maize plants than
the lower rate of 2l/ha at 6-8 WAP. Again, this was probably due to the better weed
control by the higher rates of Lumax treatment that enabled lower densities of weeds
compete with maize for resources for maize growth under the higher rates than the lower
rate. Similarly, it was reported that taller maize plants were produced by higher rates of
Atoll than lower rates at Orin-Ekiti in Nigeria (Makinde and Ogunbodede, 2007). Also,
higher leaf area index for better interception and utilization of solar radiation of maize
under 4l/ha, 6l/ha and 8l/ha Lumax treatments might have contributed to the increase in
maize height under these treatments than under the 2l/ha Lumax treatments. However,
Sakhunkhu and Faungfupong (1985) and Subhan et al. (2007) observed using different
methods of weed control that plant height was non-significantly affected by various
herbicide treatments. However Subhan et al. (2007) reported that although not
94
approaching the level of statistical significance, the taller plants (163, 160, 160 cm) were
attained in plots treated with Dual gold, Primextra gold and Atrazine when applied as
pre-emergence, while minimum plant height of 132cm was recorded in weedy check
plots. Sakhunkhu and Faungfupong (1985), Rambakudzibga et al. (2002) and Subhan et
al. (2007) reported that under field conditions, maize height was not significantly affected
by weed competition when weeds were removed as late as 8 weeks after crop emergence.
However, Rambakudzibga et al. (2002) suggested that weeds should be removed within
four weeks after crop emergence to avoid grain yield reductionsince grain yield, appeared
to be more sensitive to weed competition effects than other maize developmental
attributes.
The trends in the increase in maize height in this study revealed that the maximum
increase in height occurred from 4 to 6 WAP. At this stage, maize plants are well
established with well developed roots, root hairs and photosynthetic apparatus necessary
for tapping the growth factors in the plants’ environment (Hamayun, 2003). Nutrient
uptake increases very rapidly and coincides with a more efficient interception and
utilization of solar radiation for photosynthesis (Adjetey, 1994) and under normal
conditions, new leaves form and the young plant develops a stem which rapidly grows in
length (Guy, 1987; DARSA, 2003).
The rate of increase in maize height under all treatments which declined from 6-8 WAP
after a rapid increase from 4 to 6 WAP in both years supported the findings of Gifford
and Evans (1981) that after flowering, the reproductive sink becomes extremely
strong,and limits the assimilate partitioned for additional leaf, stem and roots growth.
95
Specifically, Gifford and Evans (1981) reiterated that in determinate species, leaf and
stem growth cease at flowering.
5.4.5 Maize Shoot Dry matter
Plant dry matter accumulation depends on the quantity of the total carbon fixed by
photosynthesis and the fraction of that carbon converted to dry matter (Norman and
Arkebaver, 1991). In addition to the presence of biotic and abiotic stresses, plant dry
matter accumulation depends on the quantity of radiation absorbed by the canopy (Kiniry
et al., 1989; Sinclair and Muchow, 1999).
Maize shoot dry matter under 4l Lumax/ha, 6l Lumax/ha, 8l Lumax/ha and Hoe-weeded
treatments were at par and greatly exceeded the dry matter under 2l Lumax/ha and
Unweeded treatments from 5 WAP to harvest in 2010 and at harvest in 2009. This was
possibly due to the better weed control and weed control efficiency resulting in lower
weed density and higher weed dry matter under the 4l Lumax/ha, 6l Lumax/ha, 8l
Lumax/ha and Hoe-weeded treatments. In addition, the lower weed competition with
maize, taller maize plants, higher leaf area index of maize, higher efficiency in
intercepting and absorbing solar radiation and partitioning of assimilate and inorganic
nutrients for enhanced dry matter production than under 2l Lumax/ha and Unweeded
treatments (Giaquinta, 1980) also contributed to the higher dry matter accumulation.
Hoe-weeding and application of Lumax caused significant increase in shoot dry matter of
maize over Unweeded treatment. These results were in line with those reported by
Ahmad et al. (1988), Kandasamy and Chandrasekhar (1998), Singh (2002) and Riaz et al.
(2007).
96
Maize shoot dry matter increased continuously from 3 WAP to harvest similar to the
trends in maize height, but negatively related to the trends in weed density. These trends
indicated that as weed densities are reduced, maize plants grow taller and produce more
dry matter.
5.5 Yield and yield components
5.5.1 100-Seed Weight
In 2010, all weed control treatments had significantly greater 100-seed weight than the
Unweeded control. The higher 100-seed weight might be due to the effective control of
weeds and reduced competition from weeds thus increase in uptake of nutrients and
thereby healthy growth and developments of crop which resulted in higher grain weight.
These results agree with previous findings of Gill et al. (1977), Ahmad et al. (1988),
Durkic and Kenezev (1996), Patel et al. (2006) and Riaz et al. (2007). Patel et al. (2006),
for example, reported that maximum test weight of 20.4g was recorded with preemergence application of atrazine at 0.50 kg a.i./ha in combination with pendimethalin at
0.25 kg a.i./ha, followed by twice hand weeding carried out at 20 and 40 DAP which was
significantly higher than the test weight for weedy check. However, in 2009 study year,
no significant difference in 100-seed weight was observed among treatments. This
observation agrees with the results of work done by Kombiok et al. (2003) and Makinde
and Ogunbodede (2007) who reported similar non-significant difference among various
treatments with respect to 100-seed weight of maize.
97
The higher 100-seed weight values obtain in 2010 as compared to those of 2009 could be
attributed to availability of higher amount of moisture to the plants as a result of higher
amount of rains during the cropping period in 2010.
5.5.2 Harvest Index
Harvest index is defined as the ratio of yield biomass to the total cumulative biomass at
harvest (Worku and Zelleke, 2007). A higher mean harvest index value in the 2009
cropping season than in 2010 may be due to many factors that might have favoured
partitioning of photosynthate to maize grain than vegetative plant part during the 2009
season. Barton (2000) obseverd that either biotic or abioticfactors could induce stress in a
plant affecting specific processeson individual leaves resulting both in a loss of
chlorophyll and in a change in its distribution pattern. Ahmad et al. (2007) attributed low
grain crop harvest index to cultivation of non-recommended crop cultivars, unapproved
seed used for sowing, late sowing, imperfect sowing methods, low plant population, poor
plant protection and proliferation of weeds, imbalanced use of fertilizer and nonavailability of water for irrigation at critical crop growth stages. Low crop harvest index
is the major cause of low crop yield. Ahmad et al. (2007) therefore, concluded that
harvest index could be used as a yardstick for determining the gap between potential and
actual yields. By definition, potential yield is the yield of a cultivar when grown in an
ideal environment, with adequate nutrients and moisture, and stresses like pests, diseases,
weeds, lodging are effectively controlled. On the other hand, actual yield is the maximum
yield which could be obtained under given environmental conditions and with available
inputs (Ahmad et al., 2007).
98
Values for harvest indexes that ranged from 0.28 to 0.42 for both years with the mean
harvest index of 0.40 in 2009 and 0.32 in 2010 were, however, lower than the range of
0.4 to 0.6 for some modern cultivars of intensively cultivated maize (Ahmad et al., 2007).
The least harvest index recorded under Unweeded treatment could be attributed to higher
partitioning of assimilates to vegetative biomass at the expense of grains (sinks).
Furthermore, the increase in values for harvest index compared to Unweeded treatment
may be attributed to adequate suppression of weed growth due to some residual herbicide
effect as well as more availability of plant nutrients to maize crop, which favoured better
utilization of photo-assimilates for grain yield formation. Similar results have been
discussed by Ahmad et al. (1988); Salisbury and Ross (1991) and Riaz et al. (2007).
5.5.3 Grain Yield
Grain yields of maize were generally higher in 2010 than in 2009 (Table 4.10). One
major factor attributable to the lower grain yield in 2009 than in 2010 was the lower total
rainfall of 316.5mm in 2009 as compared to the 494.9mm in 2010 cropping season
(Tables 4.1and 4.2). Also, the sharp drop in the volume of rainfall from 138.6mm to
45.2mm during the tasseling to grain filling stage of maize growth in 2009 might have
contributed significantly to the lesser grain yields in 2009 than during the 2010 growing
season. These findings were in line with the observations of Awuku et al. (1991), Adjetey
(1994) and Tweneboah (2000), who indicated that the tasseling to grain filling stage of
maize growth is the most sensitive period to water shortage, and any water deficit during
this stage will adversely affect grain yield.
99
Furthermore, the higher grain yields in 2010 than in 2009 might be due to minimum weed
seed bank and better eradication of weeds providing healthier environment for plant
growth during the 2010 cropping season. Through competition for nutrients, weeds can
reduce the growth and yields of maize by influencing the availability of soil water
(Thomas and Alison, 1975; Marais, 1985; Twomlow et al., 1997). These result, among
other effects, in the temporary immobilization of nutrients in the plough layer (Marais,
1985).
A significant effect of different weed control treatments was observed on grain yield of
maize during both years. When pooled, maize grain yield increased by 23-55% probably
because of effective weed control by Lumax treatment at rates 2-8l/ha and Hoe-weeded
treatment that might have significantly reduced competition for nutrients, water and solar
radiation compared with Unweeded control treatment. On their part, Chikoye et al.
(2009) reported that Lumax at five rates: 1.88-2.96 kg a.i. /ha significantly reduced weed
density and biomass and increased grain yield by 12-22%. Riaz et al. (2007)
demonstrated that hand weeding and chemical method of weed control in maize gave 3234% increase in grain yield of maize as compared to weedy check. Similarly, Jehangeri et
al. (1984) reported that application of selective herbicides provided 65 to 90% weed
control and 100 to 150% more maize grain yields than unweeded control. Other studies
(Miller et al., 1980; Fisher et al., 1980; Bially, 1995; Durkic and Knezevic, 1996; Ali et
al., 2003; Subhan et al., 2007; Gana et al., 2008) have also reported better maize grain
yield with herbicide application than weedy check.
100
The highest grain yields were in treatments with 4-8l/ha of Lumax and the Hoe weeded
control representing increased grain yield of 53-55% when pooled. Maize grain yield
from the Hoe-weeded treatment was among the highest, because of good weed control.
This is evident because of the low weed dry matter in Hoe-weeded plots. However, hoeweeding is very tedious, time consuming and takes up significant proportion (about 50 to
80%) of the total labour budget (Chikoye et al., 2002). Also, labour is scarce, during
early stages of crop growth when it is necessary for weeds to be controlled, thus making
this management option more expensive for resource-poor farmers. Untimely weeding
causes significant crop losses (Chikoye et al., 2004). In replicated trials, herbicide use
gave 11% yield advantage over traditional cultivation and saved 16 man-hours/ha or 80%
of the labour normally used for weeding (Jennings et al., 1979).
At 12WAP during both years of study, weed density and weed dry matter significantly
and negatively correlated with grain yield. The highly negative correlation of both weed
dry matter and weed density with grain yield at 12WAP supports the findings in the
present study in which maize grain yield in most plots that received Lumax preemergence herbicide and hoe-weeding was better than in the Unweeded plot because of
good weed control and low weed dry matter in those plots. These findings corroborate the
results reported by Chikoye et al. (2006) which indicated that there was a negative linear
relationship between weed dry matter and maize grain yield in both years. Chikoye et al.
(2006) also found a negative relationship between weed density and maize grain yield.
However, percentage weed control and leaf area index at 6 WAP as well as 100-seed
weight, maize shoot dry matter and weed control efficiency at harvest positively
101
correlated with grain yield during both study years. This implies that with effective and
efficient weed control, more plant nutrients are made available to the maize crop for
enhanced leaf area formation that increases solar radiation interception which favours
better utilization of photosynthate for higher grain yield.
5.6 Economic or Partial Budget Analysis
The adjustment of grain yields by 10% in the analysis was to approximate the yield that
farmers can obtain on their farms (Alimi and Manyong, 2000). This was necessary to
prevent overestimation of the returns that farmers are likely to obtain from a treatment
(Dapaah et al., 2007). In addition, the experimental fields usually have higher
management levels, smaller plot sizes, precision in harvesting and better harvesting
methods. The analysis showed that in general all treatments were economically attractive,
as they had positive net benefits. The Unweeded control treatment as expected gave the
least net benefit. Similarly, Riaz et al. (2007) reported that all the treatments in their
study gave higher net benefit as compared to the control weedy check. The 4l Lumax/ha
had the highest net benefit among the treatments because it had the highest difference
between total gross benefit and total variable cost.
The dominance analysis showed that the 6l Lumax/ha, Hoe-weeded and 8l Lumax/ha
treatments had lower net benefits but higher total variable costs than the
4lLumax/hatreatment, and therefore, were dominated by the latter. This implies that even
at a lower application rate than the 6l Lumax/ha and 8l Lumax/ha, the 4l Lumax/ha
102
treatment gave the best economic return. Hence, the 4l Lumax/ha was more profitable
than the higher rates.
Also, the dominance of the 4l Lumax/haover the Hoe-weeded treatment supports
Muthamia et al. (2001) who reported that use of herbicides resulted in significantly
greater maize grain yields and economic benefit than hand weeding in sole maize crop.
Specifically Muthamia et al. (2001) noted that the increase in yield was 25-50% with a
mean of 33%, and economic benefits of 33% from the use of herbicide weed
management compared with hand-weeding in small holder farms. Riaz et al. (2007)
specified that among chemical, mechanical and hand weeded weed control, the hand
weeding at 20 & 40 DAP treatment was dominated due to less net benefit and higher cost
that varied, so it was uneconomical treatment at the prevailing crop and herbicide prices.
Furthermore, using herbicides to reduce the drudgery of persistent weeding is most
appropriate especially in times of chronic labour shortages. Herbicides also reduce
seasonal variation in labour markets and the total labour needed for hand weeding,
stabilizing labour requirements for freeing workers to pursue higher-value opportunities
(Riches et al., 2005). Takeshita and Noritake (2001) reported that farmers in Japan used
to spend 50 hours to weed 0.1 ha by hand. In reality, a farmer used to spend 6-7 days per
0.1 ha for weed control (before herbicides). An estimated 70 million additional workers
would be required in the United States alone if hand-weeding was the only option
(Annon, 2003). Herbicides overcome these problems because they control weeds in a
way that is quicker and easier than hoe-weeding and usually requires far less man power.
Though, the Hoe-weeded treatment was dominated by the 4l Lumax/ha, the Hoe-weeded
103
treatment was more profitable than the 8l Lumax/ha because it gave MRR of 69% and
24% over the 8l Lumax/ha in 2009 and 2010 respectively.
Applying 4l Lumax/haover the 2l Lumax/ha which gave MRR of 501% and 714% in
2009 and 2010 respectively indicates that for every GH¢100 invested, for example, in
adopting 4l Lumax/ha over the 2l Lumax/ha, the farmer gets an additional gain of
GH¢401-GH¢614. Therefore, the 4l Lumax/ha treatment is recommended for high net
benefits and MRR.
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CHAPTER SIX
SUMMARY, CONCLUSIONS AND RECOMMENDATIONS
6.1 Summary
Lumax 537.5 SE at application rates 2l/ha, 4l/ha, 6l/ha and 8l/ha together with Unweeded
and Hoe-weeded treatments as the controls were studied for their influence on weed
control in maize, maize growth and yield as well as economic benefits in maize
production in field experiments conducted in 2009 and 2010.
With regards to weed control, data collected included weed score, weed density,
percentage weed control, weed flora composition, weed dry matter and weed control
efficiency. The variables observed for maize growth were percentage crop establishment,
maize height, leaf area index, days to 50% silking and shoot dry matter. For maize yield
and yield components, variables including 100 seed weight, harvest index and grain yield
were observed. Partial budget analysis was used to estimate the net benefits and marginal
rates of return to determine the economic benefit to farmers.
Results showed that although Hoe-weeded and Unweeded control treatments recorded the
highest weed score at 2 WAP, Hoe-weeded and all Lumax-treated plots gave better weed
control efficiency with
lower weed densities and weed dry matter than Unweeded
control treatment. Among the various rates of Lumax application, 4l/ha was as effective
as 6l/ha and 8l/ha in weed control. Lumax at all rates controlled Panicum maximum,
Acanthospermum hispidium effectively while Cyperus rotundus, a sedge, was not
effectively controlled.
105
In terms of percentage crop establishment in both years, and days to 50% silking in 2009,
differences among treatments were not significant. However, 4l Lumax/ha, 6l Lumax/ha,
8l Lumax/ha and Hoe-weeded treatments produced similarly taller plants with higher leaf
area index and shoot dry matter than Unweeded control during both cropping years of
study.
Differences in pooled grain yield, 100-seed weight and harvest index among 4l
Lumax/ha, 6l Lumax/ha, 8l Lumax/ha and Hoe-weeded treatments were not significant
during both cropping seasons. However, grain yield and harvest index were significantly
higher for plots treated with Lumax at 4l/ha, 6l/ha and 8l/ha and hoe-weeded plots over
the Unweeded treatment in both years.
In both years, weed density and weed dry matter highly negatively correlated with maize
grain yield. On the other hand, percentage weed control, maize leaf area index, 100 seed
weight, maize shoot dry matter and weed control efficiency had significant and highly
positive correlation with maize grain yield in both years of study.
The most promising treatment in terms of net benefit and marginal rate of returns was 4l
Lumax/ha; and as expected, the Unweeded treatment gave the least net benefit.
Compared to 4l Lumax/ha, the 6l Lumax/haand 8l Lumax/ha and Hoe-weeded treatments
had lower net benefit, but higher total variable cost, and therefore, were dominated. The
4l Lumax/ha gave marginal rates of returns of 501-714% over 2l/ha Lumax in both years.
106
6.2. Conclusions
Determination of optimum rate of application is an important consideration for lucrative
return on maize production and a safe environment. The lack of significant differences in
weed control, maize growth and grain yield among 4l Lumax/ha, 6l Lumax/ha, 8l
Lumax/ha and Hoe-weeded treatments implies that farmers adopting any of these rates of
Lumax application and hoe-weeding would have similar results. However, manual
weeding which is the predominant method of weed control by small holder farmers in the
transitional agro-ecological zone of Ghana is time consuming, laborious and very
expensive.
The results clearly indicated that the use of 4l Lumax 537.5 SE/ha produced similar weed
control, maize growth and yields as 6l Lumax/ha, 8l Lumax/ha and Hoe-weeded
treatments. The economic analysis indicated that 4l Lumax 537.5 SE/ha was the most
economically viable option to fully recommend for adoption across the transitional agroecological zone of Ghana or similar representative environments.
Pre-emergence application of Lumax 537.5 SE at 4l/ha is recommended as the optimum
rate for effective weed control, enhanced growth and high yields of maize and lucrative
economic benefits on maize production in the transitional agro-ecological zone of Ghana.
The contrast in weed control, maize growth and grain yield as affected by various rates of
Lumax 537.5 SE reported in this study for the two different years clearly shows that the
benefit of applying the herbicide are location and time specific.
107
6.3 Recommendations for Future Research
Many farmers in the transitional agro-ecological zone of Ghana grow different crops on
fields from which maize have been harvested. The residual effect of Lumax 537.5 SE on
such crops on those lands has to be investigated to ensure the safety of the herbicide on
those crops and their yields.
The efficacy of the optimum rate of application of Lumax 537.5 SE determined in the
current study could be compared with those of other pre-emergence herbicides on the
Ghanaian market for maize production in the transitional agro-ecological zone of Ghana.
The results from the comparative analysis would enable farmers to make informed
decisions on their choice of the best herbicide for maize production in the area.
The experiment should be repeated on-farm on other soil and vegetation types to observe
the behaviour of the various rates of Lumax 537.5 SE on maize production in other agroecological zones. This would facilitate the transfer of results to farmers in those areas for
easy adoption.
108
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APPENDICES
Appendix 1: Guide to Interpretation of Soil Analytical Data
Property
Phosphorus, P (ppm), (Bray 1)
<10
10-20
>20
Potassium, K (ppm)
<50
50-100
>100
Calcium, C (ppm)/Mg-0.25 Ca
<5.0
5.0-10.0
>10.0
ECEC (Cmol(+)/kg
<10
10-20
>20
Soil pH (Distilled Water Method)
<5.0
5.1-5.5
5.6-6.0
6.0-6.5
6.5-7.0
7.0-7.5
7.6-8.5
>8.5
Organic Matter (%)
<1.5
1.6-3.0
>3.0
Nitrogen (%)
<0.1
0.1-0.2
>2.0
(Soil Research Institute, 2009 and 2010)
Rank/Grade
Low
Moderate
High
Low
Moderate
High
Low
Moderate
High
Low
Moderate
High
Very Acidic
Acidic
Moderately Acidic
Slightly Acidic
Neutral
Slightly Alkaline
Alkaline
Very Alkaline
Low
Moderate
High
Low
Moderate
High
132
Appendix 2: Percentage Composition of Life Form Category and Dominant Species of Weeds at
6WAP in 2009
Treatment
Life Form Category
Grasses
Unweeded
Broadleaf weeds
Sedges
Grasses
2l
Lumax/ha
32.02
54.01
11
24.08
Sedges
64.93
6.6
Breadleaf weeds
6.92
Sedges
86.48
6l
Lumax/ha
Grasses
Broadleaf weeds
Sedges
8l
Lumax/ha
Grasses
Broadleaf weeds
Sedges
Grasses
Hoeweeded
13.96
Broadleaf weeds
Grasses
4l
Lumax/ha
% Composition
Broadleaf weeds
Sedges
6.6
6.92
86.48
3.08
6.92
90
12.25
26.75
65.7
133
Dominant Species
Echinochloa crus-galli
Rottboela conchichinensis
Sorghum halepens
Panicum maximum
Acanthospermum
hispidium
Ageratum conyzoides
Bidens pilosa
Euphorbia heterophylla
Commelina diffusa
Amaranthus spinosus
Cyperus rotundus
Rottboella
conchichinensis
Sorghum halepens
Euphorbia heterophylla
Bidens pilosa
Commelina diffusa
Cyperus rotundus
Rottboella
conchichinensis
Sorghum halepens
Commelina diffusa
Euphorbia heterophylla
Cyperus rotundus
Rottboella
conchichinensis
Commelina diffusa
Cyperus rotundus
Rottboella
conchichinensis
Commelina difusa
Cyperus rotundus
Rottboella
conchichinensis
Sorghum halepens
Panicum maximum
Echinochloa crus-galli
Euphorbia heterophylla
Amaranthus spinosus
Bidens pilosa
Commelina diffusa
Cyperus rotundus
% Composition
28
24
22
10
15
15
18
14
8
16
100
32
38
31
18
34
100
56
28
65
14
100
42
62
100
48
44
100
23
18
16
22
28
10
23
20
100
Appendix 3:Percentage Composition of Life Form Category and Dominant Species of Weeds at6 WAP in 2010
Treatment
Life Form Category
Grasses
Broadleaf weeds
%Composition
10
45
Unweeded
Dominant Species
Echinochloa crus-galli
Rottboela conchichinensis
21
Sorghum halepens
21
Panicum maximum
12
Acanthospermum hispidium
9
Boerhavia diffusa
35
Bidens pilosa
12
Euphorbia heterophylla
15
Commelina benghalensis
18
Amaranthus spinosus
45
Cyperus rotundus
100
Grasses
5
Rottboella conchichinensis
36
Echinochloa crus-galli
40
Euphorbia heterophylla
18
Bidens pilosa
10
Boerhavia diffusa
45
Broadleaf weeds
6l Lumax/ha
8l Lumax/ha
40
Commelina benghalensis
25
Sedges
55
Cyperus rotundus
100
Grasses
1
Rottboella conchichinensis
33
Echinochloa crus-galli
54
Commelina benghalensis
32
Boerhavia diffusa
55
Sedges
79
Cyperus rotundus
100
Grasses
1
Broadleaf weeds
22
Echinochloa crus-galli
Rottboella conchichinensis
Boerhavia diffusa
Commelina benghalensis
35
26
48
26
Sedges
77
Cyperus rotundus
100
Grasses
1
30
35
42
33
Breadleaf weeds
21
22
Rottboella conchichinensis
Echinochloa crus-galli
Boerhavia diffusa
Commelina benghalensis
Sedges
78
Cyperus rotundus
100
Grasses
2
Broadleaf weeds
26
Sedges
72
Rottboella conchichinensis
Sorghum halepens
Panicum maximum
Echinochloa crus-galli
Euphorbia heterophylla
Amaranthus spinosus
Boerhavia diffusa
Bidens pilosa
Commelina benghalensis
Cyperus rotundus
20
15
10
26
19
11
24
11
20
100
Broadleaf weeds
Hoe-weeded
6
Sedges
2l Lumax/ha
4l Lumax/ha
% Compositon
30
134
Appendix 4: Information used for the partial budget analysis, 2009 and 2010
Variable
Quantity/Amount
Farm gate price of maize
GH¢500/t
Cost of Lumax 537.5 SE
GH¢25/litre
Labour for Lumax application
2 mandays/ha
Labour for hauling water to mix with Lumax
1 manday/ha
Labour for 1 hoe- weeding
20 mandays/ha
Cost of Labour
GH¢5/manday
Sprayer rental
GH¢4/ha
Cost of shelling
GH¢25/t
135